This patch allows the user to disable IGMP snooping completely
through a sysfs toggle.  It also allows the user to reenable
snooping when it has been automatically disabled due to hash
collisions.  If the collisions have not been resolved however
the system will refuse to reenable snooping.
Signed-off-by: NHerbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

This patch allows the user to forcibly enable/disable ports as
having multicast routers attached.  A port with a multicast router
will receive all multicast traffic.

The value 0 disables it completely.  The default is 1 which lets
the system automatically detect the presence of routers (currently
this is limited to picking up queries), and 2 means that the port
will always receive all multicast traffic.
Signed-off-by: NHerbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

This patch adds the core functionality of IGMP snooping support
without actually hooking it up.  So this patch should be a no-op
as far as the bridge's external behaviour is concerned.

All the new code and data is controlled by the Kconfig option
BRIDGE_IGMP_SNOOPING.  A run-time toggle is also available.

The multicast switching is done using an hash table that is
lockless on the read-side through RCU.  On the write-side the
new multicast_lock is used for all operations.  The hash table
supports dynamic growth/rehashing.

The hash table will be rehashed if any chain length exceeds a
preset limit.  If rehashing does not reduce the maximum chain
length then snooping will be disabled.

These features may be added in future (in no particular order):

* IGMPv3 source support
* Non-querier router detection
* IPv6
Signed-off-by: NHerbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>