Verify that the passed mask to rxe_modify_device() is supported.

Link: https://lore.kernel.org/r/20190923104158.5331-4-kamalheib1@gmail.comSigned-off-by: Kamal Heib <kamalheib1@gmail.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>