Bluetooth: Update LTK lookup to correctly deal with SC LTKs

LTKs derived from Secure Connections based pairing are symmetric, i.e.
they should match both master and slave role. This patch updates the LTK
lookup functions to ignore the desired role when dealing with SC LTKs.

Furthermore, with Secure Connections the EDiv and Rand values are not
used and should always be set to zero. This patch updates the LTK lookup
to first use the bdaddr as key and then do the necessary verifications
of EDiv and Rand based on whether the found LTK is for SC or not.

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