IB/mlx5: Fix pkey_index length in the QP path record

Pkey index fields in the QP context path record are extended to 16
bits, as required by IB spec (version 1.3).
This change affects all QP commands which include path records.

To enable this change, moved the free adaptive routing flag bit
(free_ar) to the most significant byte of the QP path record.

Fixes: e126ba97

 ('mlx5: Add driver for Mellanox Connect-IB ...')
Signed-off-by: Noa Osherovich <noaos@mellanox.com>
Reviewed-by: Jack Morgenstein <jackm@dev.mellanox.co.il>
Signed-off-by: Leon Romanovsky <leon@kernel.org>
Signed-off-by: Doug Ledford <dledford@redhat.com>