ath10k: perform hw restart lazily

This reduces risk of races and prepares for more
hw restart fixes.

It also makes sense to perform teardown after
mac80211 starts its restart routine as it
guarantees it has stopped itself by then
(including tx queues).

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