Bluetooth: Clearly distinguish mgmt LTK type from authenticated property

On the mgmt level we have a key type parameter which currently accepts
two possible values: 0x00 for unauthenticated and 0x01 for
authenticated. However, in the internal struct smp_ltk representation we
have an explicit "authenticated" boolean value.

To make this distinction clear, add defines for the possible mgmt values
and do conversion to and from the internal authenticated value.

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