[FlySky IBUS] Fix some sensor interpretation (#4077)

Also use SNR instead RSSI for FlySky since SNR gives a better indication of signal quality and also our current implementation of RSSI warning cannot really handle negative values

radio/src/gui/480x272/model_telemetry.cpp

@@ -521,6 +521,13 @@ bool menuModelTelemetryFrsky(event_t event)
         break;
 
       case ITEM_TELEMETRY_RSSI_LABEL:
+#if defined(MULTIMODULE)
+        if (g_model.moduleData[INTERNAL_MODULE].rfProtocol == RF_PROTO_OFF &&
+          g_model.moduleData[EXTERNAL_MODULE].type == MODULE_TYPE_MULTIMODULE  &&
+          g_model.moduleData[EXTERNAL_MODULE].getMultiProtocol(false) == MM_RF_PROTO_FS_AFHDS2A)
+          lcdDrawText(y, PSTR("RSNR"));
+        else
+#endif
         lcdDrawText(MENUS_MARGIN_LEFT, y, PSTR("RSSI"));
         break;