fix some compile issue in cpp project(like WiFiMulti.h) (espressif#350)

Author: tzxespressio

libraries/WiFi/src/WiFiClient.h

@@ -23,6 +23,8 @@
 
 #include "Arduino.h"
 #include "Client.h"
+#undef min
+#undef max
 #include <memory>
 
 class WiFiClientSocketHandle;