Bluetooth: BAP: Fix notifying recv state for bonded devices

The scan_delegator_security_changed function had a few issues
that were addressed:
1) It used an internal field to check level rather than the
   value provided by the API
2) It did not treat bt_addr_le_is_bonded as a boolean return value
3) It did not properly truncate the recv state (fixed by using the
   proper function bass_notify_receive_state)

Signed-off-by: Emil Gydesen <emil.gydesen@nordicsemi.no>