UPSTREAM: ath9k: Make sure to zero status.tx_time before reporting TX status

Since ath9k reports airtime usage directly using the
ieee80211_report_airtime() callback, it shouldn't also report it using the
tx_time in status. Make sure the field is zeroed before TX status is
reported to avoid spurious airtime being accounted by bits being left over
from earlier uses of the cb.

Fixes: 89cea749 ("ath9k: Switch to mac80211 TXQ scheduling and airtime APIs")
Signed-off-by: Toke Hiland-Jrgensen <toke@redhat.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>

BUG=b:131197056
TEST=4.14-gw kernel compiles

(cherry picked from commit cc591d77)

Signed-off-by: Kan Yan <kyan@google.com>
Change-Id: I8f389fdea69e2db8c9b00d117c5b764d6eeabfc4
Reviewed-on: https://chromium-review.googlesource.com/1636904


Legacy-Commit-Queue: Commit Bot <commit-bot@chromium.org>
Reviewed-by: Julan Hsu <julanhsu@google.com>
Reviewed-by: Sean Paul <seanpaul@chromium.org>
Reviewed-by: Kan Yan <kyan@chromium.org>