The tid of 11a station with WMM disable reported by FW is 0x10 in
tx completion. The tid 16 is mapped to a NULL txq since buffer
MMPDU capbility is not supported. Then 11a station's airtime will
not be registered due to NULL txq check. As a results, airtime of
11a station keeps unchanged in debugfs system.

Mask the tid along with IEEE80211_QOS_CTL_TID_MASK to make it in
the valid range.

Hardwares tested : QCA9984
Firmwares tested : 10.4-3.10-00047
Signed-off-by: Yibo Zhao <yiboz@codeaurora.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>