mirror: stop cancelling in-flight requests on non-force cancel in READY

mirror: stop cancelling in-flight requests on non-force cancel in READY

If mirror is READY than cancel operation is not discarding the whole
result of the operation, but instead it's a documented way get a
point-in-time snapshot of source disk.

So, we should not cancel any requests if mirror is READ and
force=false. Let's fix that case.

Note, that bug that we have before this commit is not critical, as the
only .bdrv_cancel_in_flight implementation is nbd_cancel_in_flight()
and it cancels only requests waiting for reconnection, so it should be
rare case.

Fixes: 521ff8b779b11c394dbdc43f02e158dd99df308a
Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Message-Id: <20210421075858.40197-1-vsementsov@virtuozzo.com>
Signed-off-by: Max Reitz <mreitz@redhat.com>