mac80211: check if atf has been disabled in __ieee80211_schedule_txq

commit c13cf5c1 upstream.

Check if atf has been disabled in __ieee80211_schedule_txq() in order to
avoid a given sta is always put to the beginning of the active_txqs list
and never moved to the end since deficit is not decremented in
ieee80211_sta_register_airtime()

Fixes: b4809e94

 ("mac80211: Add airtime accounting and scheduling to TXQs")
Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
Acked-by: Toke Høiland-Jørgensen <toke@toke.dk>
Link: https://lore.kernel.org/r/93889406c50f1416214c079ca0b8c9faecc5143e.1608975195.git.lorenzo@kernel.org
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>