[Click] multicast support

[sgolecha at ittc.ku.edu]

Hello Eddie,

I am planning to add multicast support to click and was going thru the
documentation and the latest source code. I guess I would have to add
support for IGMP and also add a new lookup table element. I was wondering
if you could provide a minimal list of features that would be required to
support multicast.

Thanks
Santosh