IB/mlx4: Exposing modify CQ callback to uverbs layer

Exposed mlx4_ib_modify_cq to be called from ib device
verb list.

Signed-off-by: Yonatan Cohen <yonatanc@mellanox.com>
Reviewed-by: Majd Dibbiny <majd@mellanox.com>
Signed-off-by: Leon Romanovsky <leon@kernel.org>
Signed-off-by: Doug Ledford <dledford@redhat.com>