Ethernet begin with static IP - set DNS with interface name

Author: JAndrassy

libraries/Ethernet/src/Ethernet.cpp

@@ -55,7 +55,9 @@ int arduino::EthernetClass::begin(uint8_t *mac, IPAddress ip, IPAddress dns, IPA
 
   eth_if->set_dhcp(false);
   eth_if->set_network(_ip, _netmask, _gateway);
-  eth_if->add_dns_server(_dnsServer1, nullptr);
+  char if_name[5];
+  eth_if->get_interface_name(if_name);
+  eth_if->add_dns_server(_dnsServer1, if_name);
 
   auto ret = _begin(mac, timeout, responseTimeout);
   return ret;