Bluetooth: Add missing index added event on user channel failure

When the setup of user channel fails, the index added event is not sent
and will cause issues with user interaction. This problem can be easily
triggered with a LE only controller without a public address. In that
case hci_dev_open() fails and that error case is not sending an event
saying that the controller is available for normal use again.

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