ath10k: increase station kickout threshold

Since the station kickout threshold is also counting software
reries (Default sw count in firmware is 16), increasing the threshold
to try with atleast 20 data frames before kicking out the station.

Signed-off-by: Rajkumar Manoharan <rmanohar@qti.qualcomm.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>