ath6kl: Fix packet drop when ath6kl_cookie runs out

"ath6kl: Maintain virtual interface in a list" mistakenly stops the
netq only when the mode is ibss. This causes packet drops in sta mode
when the available cookies (buffer abstraction in ath6kl and also used
for tx throttling) runs out for the highest priority traffic. This patch
just fixes this regression though the original code may still need fixes
which can be addressed in separate patches.

Reported-by: Kalle Valo <kvalo@qca.qualcomm.com>
Signed-off-by: Vasanthakumar Thiagarajan <vthiagar@qca.qualcomm.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>