net/mlx5: Take only bit 24-26 of wqe.pftype_wq for page fault type

The HW spec defines only bits 24-26 of pftype_wq as the page fault type,
use the required mask to ensure that.

Fixes: d9aaed83

 ("{net,IB}/mlx5: Refactor page fault handling")
Signed-off-by: Huy Nguyen <huyn@mellanox.com>
Signed-off-by: Eli Cohen <eli@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>