Since ompi_coll_base_nbc_request_t is to be used in an
opal_free_list_t, it must be returned into a "clean" state.
So cleanup some data in the callback completion subroutines.
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@0862c409f1)
ae26957619