IGMP capabilities

G'day,

I hope you are doing well.

When looking for go IGMP capabilities we found the SerializeTo missing.

We added a little part of this IGMP capabilities, mostly IGMPv2 serialization, although the "complete" IGMP implementation remains incomplete.

https://github.com/randomizedcoder/gopacket/blob/master/layers/igmp.go#L303C21-L303C32

https://github.com/randomizedcoder/gopacket/blob/master/layers/igmp.go#L288

Anyway, I thought someone else might find this helpful.

For anyone interested in golang IGMP, I've also written an [incomplete] IGMP proxy based on gopacket.
https://github.com/randomizedcoder/goIGMP/

Thanks,
Dave