mlx4_ib: Fix the SQ size of an RC QP to support masked atomic operation

mlx4_ib: Fix the SQ size of an RC QP to support masked atomic operation

When calculating the required size of an RC QP send queue,
leave enough space for masked atomic operation (which requires
more space than "regular" atomic operation).

Signed-off-by: Dotan Barak <dotanb@dev.mellanox.co.il>
Reviewed-by: Eli Cohen <eli@mellanox.co.il>
Signed-off-by: Vladimir Sokolovsky <vlad@mellanox.com>
(Ported from Mellanox OFED 2.4)

Signed-off-by: Mukesh Kacker <mukesh.kacker@oracle.com>