cfg80211 assumes a scheduled scan is stopped synchronously. Wait for the
FW before returning to caller.
Don't do anything in the async handler in the stop-from-above flow.
There's no need to call the mac80211 sched-scan completion as the
cleanup will be automatic. Make sure the async handler is called before
the next incoming scan changes the scan_status by flushing the async
handlers after all invocations.