Bluetooth: Allow HCI User Channel usage for controllers without address

Trying to setup HCI User Channel usage for LE only controllers without
a public address or configured static address will fail with an error
saying that no address is available.

In case of HCI User Channel the requirement for a valid address is not
needed. So allow skipping this extra validation step.

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