RDMA/mlx5: Promote RSS RAW QP flags check to higher level

Move check that user didn't supplied RSS RAW QP unsupported
command flags to the function that checks all such flags.

Link: https://lore.kernel.org/r/20200427154636.381474-32-leon@kernel.org
Reviewed-by: Maor Gottlieb <maorg@mellanox.com>
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>