ath9k: rename tx_complete_work to hw_check_work

Also include common MAC alive check. This should make the hang checks
more reliable for modes where beacons are not sent and is used as a
starting point for further hang check improvements

Signed-off-by: Felix Fietkau <nbd@nbd.name>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>