generate random mac address on first start

networkDevices/W5500Device.h

@@ -2,11 +2,12 @@
 
 #include "NetworkDevice.h"
 #include <Ethernet.h>
+#include <Preferences.h>
 
 class W5500Device : public NetworkDevice
 {
 public:
-    explicit W5500Device(const String& hostname);
+    explicit W5500Device(const String& hostname, Preferences* _preferences);
     ~W5500Device();
 
     virtual void initialize();
@@ -18,7 +19,11 @@ public:
 
 private:
     void resetDevice();
+    void initializeMacAddress(byte* mac);
 
     EthernetClient* _ethClient = nullptr;
     PubSubClient* _mqttClient = nullptr;
+    Preferences* _preferences = nullptr;
+
+    byte _mac[6];
 };