net/mlx4_core: Fix leakage of SW multicast entries

When removing multicast address in B0 steering mode there is
a bug in cases where there is a single QP registered for the address,
and this QP is also promiscuous. In such cases the entry wouldn't be
deleted from the SW structure representing all Ethernet MCG entries,
but would be removed in HW. This way when driver goes to remove it
from SW and HW structures the HW deletion fails.
Moreover the same index could later be used for registering
different address, which can be Infiniband.

Signed-off-by: Yevgeny Petrilin <yevgenyp@mellanox.co.il>
Signed-off-by: Eugenia Emantayev <eugenia@mellanox.com>
Signed-off-by: Amir Vadai <amirv@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>