ath9k: Test for TID only in BlockAcks while checking tx status

ath9k: Test for TID only in BlockAcks while checking tx status

The ath9k xmit functions for AMPDUs can send frames as non-aggregate in case
only one frame is currently available. The client will then answer using a
normal Ack instead of a BlockAck. This acknowledgement has no TID stored and
therefore the hardware is not able to provide us the corresponding TID.

The TID set by the hardware in the tx status descriptor has to be seen as
undefined and not as a valid TID value for normal acknowledgements. Doing
otherwise results in a massive amount of retransmissions and stalls of
connections.

Users may experience low bandwidth and complete connection stalls in
environments with transfers using multiple TIDs.

This regression was introduced in ca21b6581ec08a828970908ef2a09316c8df2243
("ath9k: validate the TID in the tx status information").

Signed-off-by: Sven Eckelmann <sven@narfation.org>
Signed-off-by: Simon Wunderlich <siwu@hrz.tu-chemnitz.de>
Cc: stable@vger.kernel.org
Acked-by: Felix Fietkau <nbd@openwrt.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>