ath10k: prevent txrx running for too long

On multicore systems it was possible for the txrx
tasklet to keep on running for long periods of
time on a single CPU due to tx completion
processing. Another CPU could feed the running
tasklet for an indefinite amount of time.

The tasklet is now guaranteed to run a finite
amount of time and is limited by HTT CE Rx ring
depth.

This improves behavior when RPS is used on target
system and might improve TCP handling as well.

Signed-off-by: Michal Kazior <michal.kazior@tieto.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>