adv_monitor: Clear any running DeviceLost timers on power down

adv_monitor: Clear any running DeviceLost timers on power down

This patch clears any running Adv Monitor DeviceLost timers on bt power
down. It'll also invoke DeviceLost event if the device is already found
and is being tracked for the DeviceLost event.

Verified this by adding a monitor using bluetoothctl and confirming that
the DeviceLost event is getting triggered for already found device in
case of bt power down.

Reviewed-by: mcchou@google.com
Signed-off-by: Anuj Jain <anuj01.jain@samsung.com>
Signed-off-by: Ayush Garg <ayush.garg@samsung.com>