Spektrum telemetry implementation (#3659)

* Implementation of Spektrum Telemetry for the DYI Multimodule.

I can only test a subset of sensors and these look okay

* Implement conversion from Fahrenheit to Celsius

* Minor fixes for Spektrum telemetry

* Add some more sensors, show sensor ID instead of instance in the overview

radio/src/telemetry/telemetry_sensors.cpp

@@ -497,6 +497,11 @@ void setTelemetryValue(TelemetryProtocol protocol, uint16_t id, uint8_t subId, u
       case TELEM_PROTO_CROSSFIRE:
         crossfireSetDefault(index, id, instance);
         break;
+#endif
+#if defined(MULTIMODULE)
+      case TELEM_PROTO_SPEKTRUM:
+        spektrumSetDefault(index, id, subId, instance);
+        break;
 #endif
       default:
         return;
@@ -571,6 +576,10 @@ int32_t convertTelemetryValue(int32_t value, uint8_t unit, uint8_t prec, uint8_t
       // T(°F) = T(°C)×1,8 + 32
       value = 32 + (value*18) / 10;
     }
+  } else if (unit == UNIT_FAHRENHEIT) {
+    if (destUnit == UNIT_CELSIUS) {
+      value = (value - 32) * 10/18;
+    }
   }
   else {
     const UnitConversionRule * p = unitConversionTable;