Low level drivers need to be able to check incoming attributes as well as be
able to adjust their private data on queue pair modification.  Add 2 driver
callbacks, check_modify_qp and modify_qp, to facilitate this.
Signed-off-by: Ira Weiny <ira.weiny@intel.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>