Because a persistent reuqest does not free its `schedule` object
when the communication completes, the `NBC_Progress` function cannot
determine the completion using `schedule`.
Without this change, a hang occurs when the `NBC_Progress` function
is called recursively through the `NBC_Start_round` function.
Signed-off-by: KAWASHIMA Takahiro <t-kawashima@jp.fujitsu.com>
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