coll/libnbc: fixes ompi ompi_coll_libnbc_request_t parent

base ompi_coll_libnbc_request_t on top of ompi_coll_base_nbc_request_t
to correctly support the retention of datatypes/operators

This fixes a regression introduced in open-mpi/ompi@0fe756d416

Signed-off-by: Gilles Gouaillardet <gilles@rist.or.jp>

(cherry picked from commit open-mpi/ompi@f8eef0fde9)

ompi/mca/coll/libnbc/coll_libnbc_component.c

@@ -460,6 +460,6 @@ request_construct(ompi_coll_libnbc_request_t *request)
 
 
 OBJ_CLASS_INSTANCE(ompi_coll_libnbc_request_t,
-                   ompi_request_t,
+                   ompi_coll_base_nbc_request_t,
                    request_construct,
                    NULL);