Bluetooth: Add helper functions for testing bdaddr types

This patch adds two helper functions to test for valid bdaddr type
values. These will be particularely useful in the mgmt code to check
that user space has passed valid values to the kernel.

Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>
Acked-by: Marcel Holtmann <marcel@holtmann.org>
Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.co.uk>