IB/ipoib: Allow mcast packets from other VFs

With SRIOV enabled, two VFs on the same HCA which have the same port LID
and may have the same QP number. To enable receiving multicasts from
such VFs, further qualify the check: ignore the receive only if, in
addition, the packet source gid equals the receiving VF's source gid.

Signed-off-by: Eli Cohen <eli@mellanox.com>
Reviewed-by: Or Gerlitz <ogerlitz@mellanox.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>