This patch gets rid of synchronuos style of authentication/accounting.
Synchronous style of authentication/accounting produced sleeping threads
which becomes a problem when lots of sessions started/stopped and all they want authorization/accounting.

When there are many interfaces to start accel-ppp stucks on startup because kernel slowly creates raw sockets.
So starting this proccess asynchronous improves accel-ppp responsiveness

To enable this specify attr-opt82 option in [ipoe] section.
Attribute must be octet type.

ipoe: introduced attr-dhcp-lease-time option to specify radius attribute to pass dhcp lease time (attribute must be integer)

Signed-off-by: NDenys Fedoryshchenko <nuclearcat@nuclearcat.com>

Previous version used linear list of vlan monitor enabled interfaces,
this caused huge overhead in packet receive path because for each
received packet it performed search on linear list to check if vlan monitor
is enabled on input device.
Current version binds internal structure to net_device->ml_priv so search is not performed more.

Before this time accel-ppp always worked in "ip unnumbered" mode.
This option may turn this mode off (default is on)

After introduction offer-delay accel-ppp stopped to answer NAK for REQUESTs if requested session is not existing
to give chance other servers to reply. But this causes that some broken clients enter to infinite REQUEST loop.
This patch corrects this issue, so if offer-delay is not configured (means that this is only server in the net) or
after receiving few REQUESTs accel-ppp send NAK for non-existing sessions.

Wait for previous session completely terminated before continuing authorization new session.

This new option will control how to represent Called-Station-ID.
Its value maybe ifname,mac or ifname:mac.
By default mac is used to keep compatibility with old versions.
Also old option ifname-in-sid is removed from documentation, but is still supported for compatibility.

Signed-off-by: NDmitry Kozlov <xeb@mail.ru>

Signed-off-by: NDmitry Kozlov <xeb@mail.ru>

Signed-off-by: NDmitry Kozlov <xeb@mail.ru>

ipoe: early allocate interface for shared vlans (prevents different values of NAS-Port in Access-Request and Account-Request)
Signed-off-by: NDmitry Kozlov <xeb@mail.ru>

Signed-off-by: NDmitry Kozlov <xeb@mail.ru>

Wait for a full retransmission cycle after reception of a StopCCN.
Introduce STATE_FIN_WAIT to identify tunnels which have received a
StopCCN but are waiting for the disconnection timer to expire.

A tunnel can go from STATE_FIN (i.e. StopCCN has been sent, waiting for
acknowledgement) to STATE_FIN_WAIT (i.e. StopCCN has been received,
waiting for full retransmission cycle), but not the other way around.
Signed-off-by: NGuillaume Nault <g.nault@alphalink.fr>

  * Set default retransmission timeout to 1 second. Since we now have
    exponential backoff, we can afford a smaller value.

  * Add the rtimeout-cap option to set the maximum value the
    retransmission timer has to respect during exponential backoff.

  * Store the maximun number of retransmissions in tunnel's structure
    (like other retransmission parameters).

  * Describe all these changes in man page and reset them to their
    default values if they're removed from configuration file before a
    reload.
Signed-off-by: NGuillaume Nault <g.nault@alphalink.fr>

Rework the l2tp_rtimeout() callback, so that time between
retransmissions expands exponentially. This allows for faster
retransmissions without without overwhelming the peer.

A cap is set on the maximum retransmission time. For now it is set to
16 seconds.
Signed-off-by: NGuillaume Nault <g.nault@alphalink.fr>

If a peer needs to disconnect a session for which it didn't receive
any reply, it sends a CDN with no Session ID. In this case, the
Assigned Session ID AVP is the only data that can be used to find out
which session has to be closed. Though it isn't supported for now,
let's accept and ack these messages. Session will be deleted on our
side thanks to the establishment timer.
Signed-off-by: NGuillaume Nault <g.nault@alphalink.fr>

Add the recv-window option in accel-ppp.conf.
Signed-off-by: NGuillaume Nault <g.nault@alphalink.fr>

Add a fixed length receive queue to tunnels and adverdise its length to
the peer using the Receive Window Size AVP.

Incoming message handling is modified as follow:
  -Read as much messages as possible and store them in the receive queue.
   Messages are stored in order, based on their sequence number. Messages
   not fitting into the queue are discarded (doesn't happen if peer
   respects our Receive Window AVP). This is the job of the new
   l2tp_tunnel_store_msg() function. It also automatically finds out if
   there are new messages to acknowledge.

  -Once all incoming messages have been read, free acknowledged packets
   from retransmission queue (based on the highest received
   acknowledgement number).

  -Then process messages in the receive queue. This is done by
   l2tp_tunnel_reply().  Each packet is processed by
   l2tp_{tunnel,session}_recv() (or dropped in some particular cases).
   The send queue is then pushed. If there's no message in the send
   queue and an acknowledgement is necessary, a ZLB is sent instead.

  -Finally, detect if the peer has acknowledged a StopCCN. There are
   three components to this test:
     -Have we tried to send a StopCCN? Check with tunnel's state.
     -Has the StopCCN been pushed on the network? Check with tunnel's
      send queue.
     -Has the peer acknowledged the StopCCN? Check with tunnel's
      retransmission queue.

For now, l2tp_tunnel_store_msg() doesn't perform fast retransmissions.
So l2tp_retransmit() is removed.
Signed-off-by: NGuillaume Nault <g.nault@alphalink.fr>

Use stacked error labels for better extensibility.
Signed-off-by: NGuillaume Nault <g.nault@alphalink.fr>