[1/13] bridge: Add IGMP snooping support

Hi Dave:

This is a repost of exactly the same series in order to get them
back into patchworks.  I hope I have resolved your concerns about
patch number 2.  Let me know if you still have any further questions.

This series of patches adds basic IGMP support to the bridge
device.  First of all the following is not currently supported
but may be added in future:

* IGMPv3 source support (so really just IGMPv2 for now)
* Non-querier router detection
* IPv6

The series is divided into two portions:

1-5 lays the ground work and can be merged without any of the
other patches.

6-13 are the actual IGMP-specific patches.

This is a kernel-only implementation.  In future we could move
parts of this into user-space just like RTP.

Cheers,
-- 
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Email: Herbert Xu ~{PmV>HI~} [off-list ref]
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