TCP-to-RTU example: Fix cbTcpRaw

Author: emelianov

examples/Bridge/TCP-to-RTU-Simulator/TCP-to-RTU-Simulator.ino

@@ -57,7 +57,7 @@ Modbus::ResultCode cbTcpRaw(uint8_t* data, uint8_t len, void* custom) {
   Serial.printf(" Fn: %02X, len: %d \n\r", data[0], len);
 
   if (transRunning) { // Note that we can't process new requests from TCP-side while waiting for responce from RTU-side.
-    tcp.setTransactionId(transRunning); // Set transaction id as per incoming request
+    tcp.setTransactionId(src->transactionId); // Set transaction id as per incoming request
     tcp.errorResponce(IPAddress((src->ipaddr), (Modbus::FunctionCode)data[0], Modbus::EX_SLAVE_DEVICE_BUSY);
     return Modbus::EX_SLAVE_DEVICE_BUSY;
   }