fix for LAN8720 static IP

src/networkDevices/EthernetDevice.h

@@ -49,6 +49,8 @@ public:
 
     virtual void initialize();
     virtual void reconfigure();
+    virtual void update();
+
     virtual ReconnectStatus reconnect(bool force = false);
     bool supportsEncryption() override;
 
@@ -89,6 +91,8 @@ private:
     int _spi_mosi;
     uint8_t _spi_freq_mhz;
 
+    int64_t _checkIpTs = -1;
+
     eth_phy_type_t _type;
     eth_clock_mode_t _clock_mode;
     bool _use_mac_from_efuse;