chore: system resolver can autoupdate

dns/util.go

@@ -107,16 +107,7 @@ func transform(servers []NameServer, resolver *Resolver) []dnsClient {
 			ret = append(ret, newDHCPClient(s.Addr))
 			continue
 		case "system":
-			clients, err := loadSystemResolver()
-			if err != nil {
-				log.Errorln("[DNS:system] load system resolver failed: %s", err.Error())
-				continue
-			}
-			if len(clients) == 0 {
-				log.Errorln("[DNS:system] no nameserver found in system")
-				continue
-			}
-			ret = append(ret, clients...)
+			ret = append(ret, newSystemClient())
 			continue
 		case "rcode":
 			ret = append(ret, newRCodeClient(s.Addr))