Fix compilation errors for lower versions (2.x)

examples/WebSocketClient/WebSocketClient.ino

@@ -9,6 +9,7 @@
 #include <Arduino.h>
 #if ESP_ARDUINO_VERSION < ESP_ARDUINO_VERSION_VAL(3,0,0)
 #include <ETHClass2.h>       //Is to use the modified ETHClass
+#define ETH  ETH2
 #include "esp_websocket_client.h"
 #else
 #include <ETH.h>