Feature: add dhcp type dns client (#1509)

dns/util.go

@@ -117,9 +117,13 @@ func isIPRequest(q D.Question) bool {
 func transform(servers []NameServer, resolver *Resolver) []dnsClient {
 	ret := []dnsClient{}
 	for _, s := range servers {
-		if s.Net == "https" {
+		switch s.Net {
+		case "https":
 			ret = append(ret, newDoHClient(s.Addr, resolver))
 			continue
+		case "dhcp":
+			ret = append(ret, newDHCPClient(s.Addr))
+			continue
 		}
 
 		host, port, _ := net.SplitHostPort(s.Addr)