The maximum unicast datagram size /without/ link fragmentation is
4096 - 4 = 4092 (max IEEE 1394 async payload size at >= S800 bus speed,
minus unfragmented encapssulation header).  Max broadcast datagram size
without fragmentation is 8 bytes less than that (due to GASP header).

The maximum datagram size /with/ link fragmentation is 0xfff = 4095
for unicast and broadcast.  This is because the RFC 2734 fragment
encapsulation header field for datagram size is only 12 bits wide.

Fixes: 5d48f00d('firewire: net: fix maximum possible MTU')
Signed-off-by: NStefan Richter <stefanr@s5r6.in-berlin.de>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

firewire-net, like the older eth1394 driver, reduced the initial MTU to
less than 1500 octets if the local link layer controller's asynchronous
packet reception limit was lower.

This is bogus, since this reception limit does not have anything to do
with the transmission limit.  Neither did this reduction affect the TX
path positively, nor could it prevent link fragmentation at the RX path.

Many FireWire CardBus cards have a max_rec of 9, causing an initial MTU
of 1024 - 16 = 1008.  RFC 2734 and RFC 3146 allow a minimum max_rec = 8,
which would result in an initial MTU of 512 - 16 = 496.  On such cards,
IPv6 could only be employed if the MTU was manually increased to 1280 or
more, i.e. IPv6 would not work without intervention from userland.

We now always initialize the MTU to 1500, which is the default according
to RFC 2734 and RFC 3146.

On a VIA VT6316 based CardBus card which was affected by this, changing
the MTU from 1008 to 1500 also increases TX bandwidth by 6 %.
RX remains unaffected.

CC: netdev@vger.kernel.org
CC: linux1394-devel@lists.sourceforge.net
CC: Jarod Wilson <jarod@redhat.com>
Signed-off-by: NStefan Richter <stefanr@s5r6.in-berlin.de>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

Commit b3e3893e ("net: use core MTU range checking in misc drivers")
mistakenly introduced an upper limit for firewire-net's MTU based on the
local link layer controller's reception capability.  Revert this.  Neither
RFC 2734 nor our implementation impose any particular upper limit.

Actually, to be on the safe side and to make the code explicit, set
ETH_MAX_MTU = 65535 as upper limit now.

(I replaced sizeof(struct rfc2734_header) by the equivalent
RFC2374_FRAG_HDR_SIZE in order to avoid distracting long/int conversions.)

Fixes: b3e3893e('net: use core MTU range checking in misc drivers')
CC: netdev@vger.kernel.org
CC: linux1394-devel@lists.sourceforge.net
CC: Jarod Wilson <jarod@redhat.com>
Signed-off-by: NStefan Richter <stefanr@s5r6.in-berlin.de>
Acked-by: NJarod Wilson <jarod@redhat.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

firewire-net:
- set min/max_mtu
- remove fwnet_change_mtu

nes:
- set max_mtu
- clean up nes_netdev_change_mtu

xpnet:
- set min/max_mtu
- remove xpnet_dev_change_mtu

hippi:
- set min/max_mtu
- remove hippi_change_mtu

batman-adv:
- set max_mtu
- remove batadv_interface_change_mtu
- initialization is a little async, not 100% certain that max_mtu is set
  in the optimal place, don't have hardware to test with

rionet:
- set min/max_mtu
- remove rionet_change_mtu

slip:
- set min/max_mtu
- streamline sl_change_mtu

um/net_kern:
- remove pointless ndo_change_mtu

hsi/clients/ssi_protocol:
- use core MTU range checking
- remove now redundant ssip_pn_set_mtu

ipoib:
- set a default max MTU value
- Note: ipoib's actual max MTU can vary, depending on if the device is in
  connected mode or not, so we'll just set the max_mtu value to the max
  possible, and let the ndo_change_mtu function continue to validate any new
  MTU change requests with checks for CM or not. Note that ipoib has no
  min_mtu set, and thus, the network core's mtu > 0 check is the only lower
  bounds here.

mptlan:
- use net core MTU range checking
- remove now redundant mpt_lan_change_mtu

fddi:
- min_mtu = 21, max_mtu = 4470
- remove now redundant fddi_change_mtu (including export)

fjes:
- min_mtu = 8192, max_mtu = 65536
- The max_mtu value is actually one over IP_MAX_MTU here, but the idea is to
  get past the core net MTU range checks so fjes_change_mtu can validate a
  new MTU against what it supports (see fjes_support_mtu in fjes_hw.c)

hsr:
- min_mtu = 0 (calls ether_setup, max_mtu is 1500)

f_phonet:
- min_mtu = 6, max_mtu = 65541

u_ether:
- min_mtu = 14, max_mtu = 15412

phonet/pep-gprs:
- min_mtu = 576, max_mtu = 65530
- remove redundant gprs_set_mtu

CC: netdev@vger.kernel.org
CC: linux-rdma@vger.kernel.org
CC: Stefan Richter <stefanr@s5r6.in-berlin.de>
CC: Faisal Latif <faisal.latif@intel.com>
CC: linux-rdma@vger.kernel.org
CC: Cliff Whickman <cpw@sgi.com>
CC: Robin Holt <robinmholt@gmail.com>
CC: Jes Sorensen <jes@trained-monkey.org>
CC: Marek Lindner <mareklindner@neomailbox.ch>
CC: Simon Wunderlich <sw@simonwunderlich.de>
CC: Antonio Quartulli <a@unstable.cc>
CC: Sathya Prakash <sathya.prakash@broadcom.com>
CC: Chaitra P B <chaitra.basappa@broadcom.com>
CC: Suganath Prabu Subramani <suganath-prabu.subramani@broadcom.com>
CC: MPT-FusionLinux.pdl@broadcom.com
CC: Sebastian Reichel <sre@kernel.org>
CC: Felipe Balbi <balbi@kernel.org>
CC: Arvid Brodin <arvid.brodin@alten.se>
CC: Remi Denis-Courmont <courmisch@gmail.com>
Signed-off-by: NJarod Wilson <jarod@redhat.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

Replace all trans_start updates with netif_trans_update helper.
change was done via spatch:

struct net_device *d;
@@
- d->trans_start = jiffies
+ netif_trans_update(d)

Compile tested only.

Cc: user-mode-linux-devel@lists.sourceforge.net
Cc: linux-xtensa@linux-xtensa.org
Cc: linux1394-devel@lists.sourceforge.net
Cc: linux-rdma@vger.kernel.org
Cc: netdev@vger.kernel.org
Cc: MPT-FusionLinux.pdl@broadcom.com
Cc: linux-scsi@vger.kernel.org
Cc: linux-can@vger.kernel.org
Cc: linux-parisc@vger.kernel.org
Cc: linux-omap@vger.kernel.org
Cc: linux-hams@vger.kernel.org
Cc: linux-usb@vger.kernel.org
Cc: linux-wireless@vger.kernel.org
Cc: linux-s390@vger.kernel.org
Cc: devel@driverdev.osuosl.org
Cc: b.a.t.m.a.n@lists.open-mesh.org
Cc: linux-bluetooth@vger.kernel.org
Signed-off-by: NFlorian Westphal <fw@strlen.de>
Acked-by: NFelipe Balbi <felipe.balbi@linux.intel.com>
Acked-by: NMugunthan V N <mugunthanvnm@ti.com>
Acked-by: NAntonio Quartulli <a@unstable.cc>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

Now that there are no more users kill dev_rebuild_header and all of it's
implementations.

This is long overdue.
Signed-off-by: N"Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

Extend alloc_netdev{,_mq{,s}}() to take name_assign_type as argument, and convert
all users to pass NET_NAME_UNKNOWN.

Coccinelle patch:

@@
expression sizeof_priv, name, setup, txqs, rxqs, count;
@@

(
-alloc_netdev_mqs(sizeof_priv, name, setup, txqs, rxqs)
+alloc_netdev_mqs(sizeof_priv, name, NET_NAME_UNKNOWN, setup, txqs, rxqs)
|
-alloc_netdev_mq(sizeof_priv, name, setup, count)
+alloc_netdev_mq(sizeof_priv, name, NET_NAME_UNKNOWN, setup, count)
|
-alloc_netdev(sizeof_priv, name, setup)
+alloc_netdev(sizeof_priv, name, NET_NAME_UNKNOWN, setup)
)

v9: move comments here from the wrong commit
Signed-off-by: NTom Gundersen <teg@jklm.no>
Reviewed-by: NDavid Herrmann <dh.herrmann@gmail.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

"dev" and "net" are NULL when alloc_netdev() is failed.
So just unlock and return an error.
Signed-off-by: NDaeseok Youn <daeseok.youn@gmail.com>
Signed-off-by: NStefan Richter <stefanr@s5r6.in-berlin.de>

Commit 8408dc1c "firewire: net: use dev_printk API" introduced a
use-after-free in a failure path.  fwnet_transmit_packet_failed(ptask)
may free ptask, then the dev_err() call dereferenced it.  The fix is
straightforward; simply reorder the two calls.
Reported-by: NDan Carpenter <dan.carpenter@oracle.com>
Cc: stable@vger.kernel.org # v3.4+
Signed-off-by: NStefan Richter <stefanr@s5r6.in-berlin.de>

FireWire upper layer drivers are converted from generic
    struct driver.probe() and .remove()
to bus-specific
    struct fw_driver.probe() and .remove().

The new .probe() adds a const struct ieee1394_device_id *id argument,
indicating the entry in the driver's device identifiers table which
matched the fw_unit to be probed.  This new argument is used by the
snd-firewire-speakers driver to look up device-specific parameters and
methods.  There is at least one other FireWire audio driver currently in
development in which this will be useful too.

The new .remove() drops the unused error return code.

Although all in-tree drivers are being converted to the new methods,
support for the old methods is left in place in this commit.  This
allows public developer trees to merge this commit and then move to the
new fw_driver methods.
Signed-off-by: NStefan Richter <stefanr@s5r6.in-berlin.de>
Acked-by: Clemens Ladisch <clemens@ladisch.de> (for sound/firewire/)
Cc: Peter Hurley <peter@hurleysoftware.com> (for drivers/staging/fwserial/)

These are redundant to log messages from the mm core.
Signed-off-by: NStefan Richter <stefanr@s5r6.in-berlin.de>

Add a new constant ETH_P_802_3_MIN, the minimum ethernet type for
an 802.3 frame. Frames with a lower value in the ethernet type field
are Ethernet II.

Also update all the users of this value that David Miller and
I could find to use the new constant.

Also correct a bug in util.c. The comparison with ETH_P_802_3_MIN
should be >= not >.

As suggested by Jesse Gross.

Compile tested only.

Cc: David Miller <davem@davemloft.net>
Cc: Jesse Gross <jesse@nicira.com>
Cc: Karsten Keil <isdn@linux-pingi.de>
Cc: John W. Linville <linville@tuxdriver.com>
Cc: Johannes Berg <johannes@sipsolutions.net>
Cc: Bart De Schuymer <bart.de.schuymer@pandora.be>
Cc: Stephen Hemminger <stephen@networkplumber.org>
Cc: Patrick McHardy <kaber@trash.net>
Cc: Marcel Holtmann <marcel@holtmann.org>
Cc: Gustavo Padovan <gustavo@padovan.org>
Cc: Johan Hedberg <johan.hedberg@gmail.com>
Cc: linux-bluetooth@vger.kernel.org
Cc: netfilter-devel@vger.kernel.org
Cc: bridge@lists.linux-foundation.org
Cc: linux-wireless@vger.kernel.org
Cc: linux1394-devel@lists.sourceforge.net
Cc: linux-media@vger.kernel.org
Cc: netdev@vger.kernel.org
Cc: dev@openvswitch.org
Acked-by: NMauro Carvalho Chehab <mchehab@redhat.com>
Acked-by: NStefan Richter <stefanr@s5r6.in-berlin.de>
Signed-off-by: NSimon Horman <horms@verge.net.au>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

Signed-off-by: NYOSHIFUJI Hideaki <yoshfuji@linux-ipv6.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

Inspection of upper layer protocol is considered harmful, especially
if it is about ARP or other stateful upper layer protocol; driver
cannot (and should not) have full state of them.

IPv4 over Firewire module used to inspect ARP (both in sending path
and in receiving path), and record peer's GUID, max packet size, max
speed and fifo address.  This patch removes such inspection by extending
our "hardware address" definition to include other information as well:
max packet size, max speed and fifo.  By doing this, The neighbour
module in networking subsystem can cache them.

Note: As we have started ignoring sspd and max_rec in ARP/NDP, those
      information will not be used in the driver when sending.

When a packet is being sent, the IP layer fills our pseudo header with
the extended "hardware address", including GUID and fifo.  The driver
can look-up node-id (the real but rather volatile low-level address)
by GUID, and then the module can send the packet to the wire using
parameters provided in the extendedn hardware address.

This approach is realistic because IP over IEEE1394 (RFC2734) and IPv6
over IEEE1394 (RFC3146) share same "hardware address" format
in their address resolution protocols.

Here, extended "hardware address" is defined as follows:

union fwnet_hwaddr {
	u8 u[16];
	struct {
		__be64 uniq_id;		/* EUI-64			*/
		u8 max_rec;		/* max packet size		*/
		u8 sspd;		/* max speed			*/
		__be16 fifo_hi;		/* hi 16bits of FIFO addr	*/
		__be32 fifo_lo;		/* lo 32bits of FIFO addr	*/
	} __packed uc;
};

Note that Hardware address is declared as union, so that we can map full
IP address into this, when implementing MCAP (Multicast Cannel Allocation
Protocol) for IPv6, but IP and ARP subsystem do not need to know this
format in detail.

One difference between original ARP (RFC826) and 1394 ARP (RFC2734)
is that 1394 ARP Request/Reply do not contain the target hardware address
field (aka ar$tha).  This difference is handled in the ARP subsystem.

CC: Stephan Gatzka <stephan.gatzka@gmail.com>
Signed-off-by: NYOSHIFUJI Hideaki <yoshfuji@linux-ipv6.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

Stefan Richter <stefanr@s5r6.in-berlin.de> says:
| As far as I can tell, it would be best to ignore max_rec and sspd from ARP
| and NDP but keep using the respective information from firewire-core
| instead (handed over by fwnet_probe()).
|
| Why?  As I noted earlier, RFC 2734:1999 and RFC 3146:2001 were apparently
| written with a too simplistic notion of IEEE 1394 bus topology, resulting
| in max_rec and sspd in ARP-1394 and NDP-1394 to be useless, IMO.
|
| Consider a bus like this:
|
|     A ---- B ==== C
|
| A, B, C are all IP-over-1394 capable nodes.  ---- is an S400 cable hop,
| and ==== is an S800 cable hop.
|
| In case of unicasts or multicasts in which node A is involved as
| transmitter or receiver, as well as in case of broadcasts, the speeds
| S100, S200, S400 work and speed S400 is optimal.
|
| In case of anything else, IOW in case of unicasts or multicasts in which
| only nodes B and C are involved, the speeds S100, S200, S400, S800 work
| and speed S800 is optimal.
|
| Clearly, node A should indicate sspd = S400 in its ARP or NDP packets.
| But which sspd should nodes B and C set there?  Maybe they set S400, which
| would work but would waste half of the available bandwidth in the second
| case.  Or maybe they set S800, which is OK in the second case but would
| prohibit any communication with node A if blindly taken for correct.
|
| On the other hand, firewire-core *always* gives us the correct and optimum
| peer-to-peer speed and asynchronous packet payload, no matter how simple
| or complex the bus topology is and no matter in which temporal order nodes
| join the bus and are discovered.

CC: Stefan Richter <stefanr@s5r6.in-berlin.de>
Signed-off-by: NYOSHIFUJI Hideaki <yoshfuji@linux-ipv6.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

Allocate FIFO address before registering net_device.
This is preparation to change the pseudo hardware address format
for firewire devices to include the offset of the FIFO for receipt
of unicast datagrams, instead of mangling ARP/NDP messages in the
driver layer.
Signed-off-by: NYOSHIFUJI Hideaki <yoshfuji@linux-ipv6.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

Send L2 multicast packet via GASP (Global asynchronous stream packet) by
seeing the multicast bit in the L2 hardware address, not by seeing upper-
layer protocol address.
Signed-off-by: NYOSHIFUJI Hideaki <yoshfuji@linux-ipv6.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

Signed-off-by: NYOSHIFUJI Hideaki <yoshfuji@linux-ipv6.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

Since those resources are allocated on ifup, relsase them on ifdown.
Signed-off-by: NYOSHIFUJI Hideaki <yoshfuji@linux-ipv6.org>
Signed-off-by: NStefan Richter <stefanr@s5r6.in-berlin.de>

Signed-off-by: NYOSHIFUJI Hideaki <yoshfuji@linux-ipv6.org>
Signed-off-by: NStefan Richter <stefanr@s5r6.in-berlin.de>

Signed-off-by: NYOSHIFUJI Hideaki <yoshfuji@linux-ipv6.org>
Signed-off-by: NStefan Richter <stefanr@s5r6.in-berlin.de>

Signed-off-by: NYOSHIFUJI Hideaki <yoshfuji@linux-ipv6.org>
Signed-off-by: NStefan Richter <stefanr@s5r6.in-berlin.de>

dev->broadcast_rcv_context is always non-NULL if dev->broadcast_state is
not FWNET_BROADCAST_ERROR.
Signed-off-by: NYOSHIFUJI Hideaki <yoshfuji@linux-ipv6.org>
Signed-off-by: NStefan Richter <stefanr@s5r6.in-berlin.de>

firewire net: Clear dev->broadcast_rcv_context and dev->broadcast_state after destruction of context.

Clear dev->broadcast_rcv_context to NULL and set dev->broadcast_state
to FWNET_BROADCAST_ERROR after descruction of broadcast context.
Signed-off-by: NYOSHIFUJI Hideaki <yoshfuji@linux-ipv6.org>
Signed-off-by: NStefan Richter <stefanr@s5r6.in-berlin.de>

Signed-off-by: NYOSHIFUJI Hideaki <yoshfuji@linux-ipv6.org>
Signed-off-by: NStefan Richter <stefanr@s5r6.in-berlin.de>

Signed-off-by: NYOSHIFUJI Hideaki <yoshfuji@linux-ipv6.org>
Signed-off-by: NStefan Richter <stefanr@s5r6.in-berlin.de>

Signed-off-by: NYOSHIFUJI Hideaki <yoshfuji@linux-ipv6.org>
Signed-off-by: NStefan Richter <stefanr@s5r6.in-berlin.de>

Signed-off-by: NYOSHIFUJI Hideaki <yoshfuji@linux-ipv6.org>
Signed-off-by: NStefan Richter <stefanr@s5r6.in-berlin.de>

fwnet_broadcast_start() try to register address handler at first
if it was not registered yet; dev->local_fifo ==
FWNET_NO_FIFO_ADDR.

Since dev->local_info not changed if fw_core_add_address_hander()
has failed, we do not need to set dev->local_info to
FWNET_NO_FIFO_ADDR.
Signed-off-by: NYOSHIFUJI Hideaki <yoshfuji@linux-ipv6.org>
Signed-off-by: NStefan Richter <stefanr@s5r6.in-berlin.de>

Signed-off-by: NYOSHIFUJI Hideaki <yoshfuji@linux-ipv6.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

It is wrong to set skb->ip_summed to CHECKSUM_UNNECESSARY unless
the device has already checked it.
Signed-off-by: NYOSHIFUJI Hideaki <yoshfuji@linux-ipv6.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

The variable card is initialized but never used
otherwise, so remove the unused variable.
Signed-off-by: NWei Yongjun <yongjun_wei@trendmicro.com.cn>
Signed-off-by: NStefan Richter <stefanr@s5r6.in-berlin.de>

This patch fixes both the transmit and receive portion of sending
fragmented mutlicast and broadcast packets.

The transmit section was broken because the offset for INTFRAG and
LASTFRAG packets were just miscalculated by IEEE1394_GASP_HDR_SIZE (which
was reserved with skb_push() in fwnet_send_packet).

The receive section was broken because in fwnet_incoming_packet is a call
to fwnet_peer_find_by_node_id(). Called with generation == -1 it will
not find a peer and the partial datagrams are associated to a peer.

[Stefan R:  The fix to use context->card->generation is not perfect.
It relies on the IR tasklet which processes packets from the prior bus
generation to run before the self-ID-complete worklet which sets the
current card generation.  Alas, there is no simple way of a race-free
implementation.  Let's do it this way for now.]
Signed-off-by: NStephan Gatzka <stephan.gatzka@gmail.com>
Cc: stable <stable@vger.kernel.org>
Signed-off-by: NStefan Richter <stefanr@s5r6.in-berlin.de>

Change the log line prefix from "firewire_net: " to "net firewire0: "
etc. for the case that several RFC 2734 interfaces are being used in the
same machine.

Note, the netdev_printk API is not very useful to firewire-net.
netdev_notice(net, "abc\n") would result in irritating messages like
"firewire_ohci 0000:0a:00.0: firewire0: abc".  Nor would a dev_printk on
the fw_unit.device to which firewire-net is being bound be useful,
because there are generally multiple ones of those per interface (from
all RFC 2734 peers on the bus, the local node being only one of them).

In the initialization message of each interface, log the PCI device
name of the card which is parent of the netdevice instead of the GUID
of the peer which was semi-randomly used to establish the netdevice.
Signed-off-by: NStefan Richter <stefanr@s5r6.in-berlin.de>

On second thought, there is little reason to have driver name differ
from module name.  Therefore, change
    /sys/bus/firewire/drivers/net
    /sys/bus/firewire/devices/fw0.0/driver -> [...]/net
    /sys/module/firewire_net/drivers/firewire:net
to
    /sys/bus/firewire/drivers/firewire_net
    /sys/bus/firewire/devices/fw0.0/driver -> [...]/firewire_net
    /sys/module/firewire_net/drivers/firewire:firewire_net
It is redundant but consistent with firewire-sbp2's recently changed
driver name.

I don't see this anywhere used, so it should not matter either way.
Signed-off-by: NStefan Richter <stefanr@s5r6.in-berlin.de>

Change memory region to ohci "middle address space". This effectively
reduces the number of packets by 50%.

[Stefan R.:]  This eliminates 1394 ack packets and improved throughput
by a few percent in some tests with an S400a connection with and without
gap count optimization.  Since firewire-net taxes the AR-req DMA unit of
a FireWire controller much more than firewire-sbp2 (which uses the
middle address space with PCI posted writes too), this commit also
changes a related error printk into a ratelimited one as a precaution.

Side note:  The IPv4-over-1394 drivers of Mac OS X 10.4, Windows XP SP3,
and the Thesycon 1394 bus driver for Windows all use the middle address
space too.
Signed-off-by: NStephan Gatzka <stephan@gatzka.org>
Signed-off-by: NStefan Richter <stefanr@s5r6.in-berlin.de>

Use kernel.h's convenience macros.  Also omit a printk that should never
happen and won't matter much if it ever happened.
Signed-off-by: NStefan Richter <stefanr@s5r6.in-berlin.de>

Signed-off-by: NDavid S. Miller <davem@davemloft.net>

Fixing a deprecation, replacing __attribute__((packed)) with __packed.
It was deprecated for portability, specifically to avoid GCC specific
code.  See commit 82ddcb04.
Signed-off-by: NAugust Lilleaas <august@augustl.com>
Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de> (added include compiler.h)

When queueing iso packets, the run time is dominated by the two
MMIO accesses that set the DMA context's wake bit.  Because most
drivers submit packets in batches, we can save much time by
removing all but the last wakeup.

The internal kernel API is changed to require a call to
fw_iso_context_queue_flush() after a batch of queued packets.
The user space API does not change, so one call to
FW_CDEV_IOC_QUEUE_ISO must specify multiple packets to take
advantage of this optimization.

In my measurements, this patch reduces the time needed to queue
fifty skip packets from userspace to one sixth on a 2.5 GHz CPU,
or to one third at 800 MHz.
Signed-off-by: NClemens Ladisch <clemens@ladisch.de>
Signed-off-by: NStefan Richter <stefanr@s5r6.in-berlin.de>