IB/mlx5: Set uid as part of MCG commands

Set uid as part of MCG commands so that the firmware can manage the
MCG object in a secured way.

Signed-off-by: Yishai Hadas <yishaih@mellanox.com>
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>