Make all Wifi code disappear if Wifi is not enabled.

WifiInterface.cpp

@@ -1,7 +1,8 @@
 /*
     © 2020, Chris Harlow. All rights reserved.
+    © 2020, Harald Barth.
 
-    This file is part of Asbelos DCC API
+    This file is part of CommandStation-EX
 
     This is free software: you can redistribute it and/or modify
     it under the terms of the GNU General Public License as published by
@@ -17,8 +18,9 @@
     along with CommandStation.  If not, see <https://www.gnu.org/licenses/>.
 */
 
+#include "WifiInterface.h"        /* config.h and defines.h included here */
+#ifdef WIFI_ON                    /* from config.h and defines.h          */
 #include <avr/pgmspace.h>
-#include "WifiInterface.h"
 #include "DIAG.h"
 #include "StringFormatter.h"
 #include "WiThrottle.h"
@@ -400,3 +402,4 @@ void WifiInterface::loop() {
   loopTimeoutStart = millis();
   loopstate = 10; // non-blocking loop waits for > before sending
 }
+#endif // WIFI_ON