ble_svc_lls_on_gap_disconnect() function

This function is the crux of the link loss service. The application developer must call this function inside the gap event callback function when a BLE_GAP_EVENT_DISCONNECT event is received and pass the disconnect reason into this function. Here, we then check if the disconnect reason is due to a timout, and if so, we call the ble_svc_lls_event_fn callback with the current alert level. The actual alert implementation is left up to the developer.