Bluetooth: mgmt: multi-adv for mgmt_reenable_advertising()

During service discovery, advertising will be disabled. This patch
ensures that it is correctly being re-enabled, both for configuration
made via set advertising and add advertising, once the scanning
times out.

Signed-off-by: Florian Grandel <fgrandel@gmail.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>