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)
b37c85dcca