Bluetooth: Ignore ADV_DIRECT_IND attempts from unknown devices

Unconditionally connecting to devices sending ADV_DIRECT_IND when
the controller is in CONNECTABLE mode is a feature that is not
fully working. The background scanning trigger for this has been
removed, but the statement allowing it to happen in case some
other part triggers is still present. So remove that code part
as well to avoid unwanted connections.

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