RDMA/uverbs: Ensure validity of current QP state value

The QP state is internal enum which is checked at the driver
level by calling to ib_modify_qp_is_ok(). Move this check closer
to user and leave kernel users to be checked by compiler.

Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Reviewed-by: Dennis Dalessandro <dennis.dalessandro@intel.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>