mac80211: minstrel_ht: don't use control.flags in TX status path

Sujith reports that my commit af61a165187bb94b1dc7628ef815c23d0eacf40b
("mac80211: add control port protocol TX control flag") broke ath9k
(aggregation). The reason is that I made minstrel_ht use the flag in
the TX status path, where it can have been overwritten by the driver.
Since we have no more space in info->flags, revert that part of the
change for now, until we can reshuffle the flags or so.

Reported-by: Sujith Manoharan <c_manoha@qca.qualcomm.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>