UDP6 Multicast Bug found in kernel.

[Kyle Butt]

In trying to get dhcpv6 running on my new router, I found that udp6 multicasct
packets weren't being delivered to userland clients. I could see them via a
non-promiscuous tcpdump, I could ping the multicast address while the process
using it was active, and I could see the associations via ifmcstatus.

I looked in the kernel and found something suspicious. Attached is a patch.

Let me know what you think.

Kyle