make it compile on all default platforms

EXmDNS.cpp

@@ -20,6 +20,7 @@
 
 #include <Arduino.h>
 #include "EthernetInterface.h"
+#ifdef DO_MDNS
 #include "EXmDNS.h"
 
 // fixed values for mDNS
@@ -193,3 +194,4 @@ void MDNS::run() {
   _udp->flush();
   // 
 }
+#endif //DO_MDNS

EXmDNS.h

@@ -17,7 +17,7 @@
  *  You should have received a copy of the GNU General Public License
  *  along with CommandStation.  If not, see <https://www.gnu.org/licenses/>.
  */
-
+#ifdef DO_MDNS
 #define BROADCASTTIME 15 //seconds
 
 typedef enum _MDNSServiceProtocol_t 
@@ -41,3 +41,4 @@ private:
   char* _serviceProto;
   int _servicePort;
 };
+#endif //DO_MDNS

EthernetInterface.cpp

@@ -32,10 +32,11 @@
 #include "WiThrottle.h"
 #include "DCCTimer.h"
 
+#ifdef DO_MDNS
 #include "EXmDNS.h"
-#define DO_MDNS
 EthernetUDP udp;
 MDNS mdns(udp);
+#endif
 
 //extern void looptimer(unsigned long timeout, const FSH* message);
 #define looptimer(a,b)

EthernetInterface.h

@@ -31,13 +31,16 @@
 #define EthernetInterface_h
 
 #include "defines.h"
+#if ETHERNET_ON == true
 #include "DCCEXParser.h"
 #include <Arduino.h>
 //#include <avr/pgmspace.h>
 #if defined (ARDUINO_TEENSY41)
  #include <NativeEthernet.h>         //TEENSY Ethernet Treiber
  #include <NativeEthernetUdp.h>   
+ #ifndef MAX_SOCK_NUM
  #define MAX_SOCK_NUM 4
+ #endif
 #elif defined (ARDUINO_NUCLEO_F429ZI) || defined (ARDUINO_NUCLEO_F439ZI) || defined (ARDUINO_NUCLEO_F4X9ZI)
  #include <LwIP.h>
 //  #include "STM32lwipopts.h"
@@ -46,6 +49,7 @@
  extern "C" struct netif gnetif;
  #define STM32_ETHERNET
  #define MAX_SOCK_NUM MAX_NUM_TCP_CLIENTS
+ #define DO_MDNS
 #else
  #include "Ethernet.h"
 #endif
@@ -77,5 +81,5 @@ class EthernetInterface {
     static void dropClient(byte socketnum);
     
 };
-
+#endif // ETHERNET_ON
 #endif