AP_RCTelemetry: add RC option to report CRSF LQ as RSSI

Co-author: Jules Gilson <julesgilson@yahoo.co.uk>

libraries/AP_RCTelemetry/AP_CRSF_Telem.cpp

@@ -171,6 +171,12 @@ void AP_CRSF_Telem::process_rf_mode_changes()
     if (_telem_last_report_ms == 0 && !uart->is_dma_enabled()) {
         gcs().send_text(MAV_SEVERITY_WARNING, "CRSF: running on non-DMA serial port");
     }
+    // note if option was set to show LQ in place of RSSI
+    bool current_lq_as_rssi_active = bool(rc().use_crsf_lq_as_rssi());
+    if(_telem_last_report_ms == 0 || _noted_lq_as_rssi_active != current_lq_as_rssi_active){
+        _noted_lq_as_rssi_active = current_lq_as_rssi_active;
+        gcs().send_text(MAV_SEVERITY_INFO, "CRSF: RSSI now displays %s", current_lq_as_rssi_active ? " as LQ" : "normally");
+    }
     // report a change in RF mode or a chnage of more than 10Hz if we haven't done so in the last 5s
     if ((now - _telem_last_report_ms > 5000) &&
         (_telem_rf_mode != current_rf_mode || abs(int16_t(_telem_last_avg_rate) - int16_t(_scheduler.avg_packet_rate)) > 25)) {

libraries/AP_RCTelemetry/AP_CRSF_Telem.h

@@ -351,6 +351,8 @@ private:
     bool _vtx_power_change_pending;
     bool _vtx_options_change_pending;
 
+    bool _noted_lq_as_rssi_active;
+
     static AP_CRSF_Telem *singleton;
 };