Bluetooth: Add structures for the new LTK exchange messages

This defines two new messages, one event that will inform
userspace that a new Long Term Key was exchanged and one that
will allow userspace to load LTKs into the kernel.

Besides the information necessary for the restablishement of
the secure link, we added some extra information: "authenticated"
that informs if the key can be used to establish an authenticated
link, and "master" that informs the role in that the key should
be used.

Signed-off-by: Vinicius Costa Gomes <vinicius.gomes@openbossa.org>
Acked-by: Marcel Holtmann <marcel@holtmann.org>
Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>