Plane: Adding Logging of RSSI data.

ArduPlane/Log.cpp

@@ -444,6 +444,9 @@ void Plane::Log_Write_RC(void)
 {
     DataFlash.Log_Write_RCIN();
     DataFlash.Log_Write_RCOUT();
+    if (rssi.enabled()) {
+        DataFlash.Log_Write_RSSI(rssi);
+    }
 }
 
 void Plane::Log_Write_Baro(void)