ath10k: fix initial radar detection logic

This fixes a problem of initial radar detection
(CAC) being stuck and blocking Rx in some cases
until all interfaces were brought down.

For userspace this meant first run of hostapd
would perform CAC but due to filtered Rx no
clients would associate. Subsequent runs of
hostapd would not perform CAC (as it was already
done) and would associate clients.

This also makes sure radar detection is performed
when bandwidth is widened. Before if 20MHz CAC was
performed then 40MHz CAC wouldn't start monitor
vdev effectively disabling initial radar
detection.

A driver should just start/stop radar detection
based on hw->conf.radar_enabled. However, since
ath10k needs to start a monitor vdev for the
initial radar detection special care needs to be
applied.

While at it cleanup the code a bit.

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