We need to return a persistent request.
`ompi_request_empty` is not a persistent request.
Signed-off-by: KAWASHIMA Takahiro <t-kawashima@jp.fujitsu.com>
Until the MPI Forum decides to add the persistent collective
communication request feature to the MPI Standard, these functions
are supported through MPI extensions with the `MPIX_` prefix.
Only C bindings are supported currently.
Signed-off-by: KAWASHIMA Takahiro <t-kawashima@jp.fujitsu.com>
