Bluetooth: Move local identity address setting to a central place

Any time hci_conn_add is used for an LE connection we need to ensure
that the local identity address is correctly described in the src and
src_type variables. This patch moves setting these values directly into
hci_conn_add so that callers don't have to duplicate the effort
themselves.

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