Bluetooth: Use random address if public address is not available

For single mode LE-only controllers, it is possible that they come
without a public address. If a public address is not available,
then use the random address for connection establishment and
scanning.

Signed-off-by: Marcel Holtmann <marcel@holtmann.org>
Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>