[ath_rate_sample] Fix correct status when completing frames with short failures.

My preivous logic was a bit wrong. This caused transmissions that failed due
to a mix of short and long retries to count intermediate rates as OK if the
LONG retry count indicated some retries had made it to this intermediate rate,
but the SHORT retry count was the one that caused the whole transmit to fail.

Now status is passed in again - and this is the status for the whole transmission -
and then update_stats() does some quick math to see if the current transmission
series hit its long retry count or not before updating things as a success
or failure.