IB/rdmavt: Add query gid stub

The handler for query gid operates along the same lines as the query pkey
handler. The driver will take care to keep the guid table updated.

Reviewed-by: Mike Marciniszyn <mike.marciniszyn@intel.com>
Reviewed-by: Ira Weiny <ira.weiny@intel.com>
Signed-off-by: Dennis Dalessandro <dennis.dalessandro@intel.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>