Add ifdef to Modbus server error message printing

Software/src/lib/eModbus-eModbus/ModbusServerRTU.cpp

@@ -256,7 +256,9 @@ void ModbusServerRTU::serve(ModbusServerRTU *myServer) {
       if (request[0] != TIMEOUT) {
         // Any other error could be important for debugging, so print it
         ModbusError me((Error)request[0]);
+        #ifdef DEBUG_VIA_USB
         LOG_E("RTU receive: %02X - %s\n", (int)me, (const char *)me);
+        #endif //DEBUG_VIA_USB
       }
     }
     // Give scheduler room to breathe