Bluetooth: host: Fix advertise stop in adv_timeout()

Call bt_le_adv_stop() if adv == bt_dev.adv (Meaning it is the legacy
advertiser and was started with bt_le_adv_start()), otherwise use
bt_le_ext_adv_stop(), because it was started with bt_le_ext_adv_start().

Failing to stop advertising shouldn't result in assert.

Signed-off-by: Michał Narajowski <michal.narajowski@codecoup.pl>