Bluetooth: Fix enabling advertising for central role

When disconnecting the advertising shall be re-enabled only when the
connection role is slave/peripheral as the central role use advertising
to connect it could end up enabling the instance 0x00 if there are other
advertising instances.

Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>