ath9k: add additional checks for the baseband hang detection

Since even with the latest changes the false positive issue of the baseband
hang check is not fully solved yet, additional checks are needed.
If the baseband hang occurs, the rx_clear signal will be stuck to high, so
we can use the cycle counters to confirm it.
With this patch, a hardware reset is only triggered if the baseband hang
check returned true three times in a row, with a beacon interval between
each check and if the busy time was also 99% or more during the check
intervals.

Signed-off-by: Felix Fietkau <nbd@openwrt.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>