IB/mlx4: Generate GID change events in IBoE code

IBoE doesn't use LIDs.  Use the GID change event to update the IB core
cache for addition/deletion of GIDs.

Signed-off-by: Eli Cohen <eli@mellanox.co.il>
Signed-off-by: Or Gerlitz <ogerlitz@mellanox.co.il>
Signed-off-by: Roland Dreier <roland@purestorage.com>