RDMA/mlx5: Combine copy of create QP command in RSS RAW QP

Change the create QP flow to handle all copy_from_user() operations in
one place.

Link: https://lore.kernel.org/r/20200427154636.381474-23-leon@kernel.orgReviewed-by: Maor Gottlieb <maorg@mellanox.com>
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>