Source-specific multicast

[Bruce M Simpson]

I am very close to merging support for RFC 3678 to -CURRENT.  I will 
make a patch available before I commit.

The only userland consumer in the tree which is likely to be affected by 
the removal of ip_multicast_if() from the kernel is routed, which I will 
update to use the new setsourcefilter() API.

The SSM code does change some of the coupling between sockets and IGMP, 
and changes some logic in udp_input; strict multicast membership becomes 
the default. For systems which deal with many multicast sockets and 
traffic, they may benefit from an additional hash table. I haven't 
finished touching the raw IP input path.

Given current looming commitments I'm open to someone volunteering to 
finish the work of merging IGMPv3 and MLDv2, or possibly to fund the work.

I wish to get at least the socket part of ASM/SSM merged before I come 
back to Yar's PR with vlan and pfsync, which I have not had reason to 
investigate thoroughly; I have had no further reports of problems with 
carp(4) in -CURRENT.

regards,
BMS