IB/mlx5: Fix ABI alignment to 64 bit

Struct mlx5_ib_striding_rq_caps was not aligned to 64 bit as
it should have been. Add a 32 bit reserved field.

Fixes: b4f34597 ('IB/mlx5: Expose multi-packet RQ capabilities')
Signed-off-by: Noa Osherovich <noaos@mellanox.com>
Reviewed-by: Yishai Hadas <yishaih@mellanox.com>
Signed-off-by: Leon Romanovsky <leon@kernel.org>
Signed-off-by: Doug Ledford <dledford@redhat.com>