genetlink: remove family pointer from genl_multicast_group

There's no reason to have the family pointer there since it
can just be passed internally where needed, so remove it.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --cc include/net/genetlink.h
Simple merge

diff --cc net/netlink/genetlink.c
Simple merge