This patch fixes the multicast group matching for 
IP_DROP_MEMBERSHIP, similar to the IP_ADD_MEMBERSHIP fix in a prior
patch. Groups are identifiedby <group address,interface> and including
the interface address in the match will fail if a leave-group is done
by address when the join was done by index, or if different addresses
on the same interface are used in the join and leave.
Signed-off-by: NDavid L Stevens <dlstevens@us.ibm.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>