DNS: Fix wrong protocol parse (#5232)

Co-authored-by: 风扇滑翔翼 <[email protected]>

app/dns/nameserver_quic.go

@@ -146,7 +146,7 @@ func (s *QUICNameServer) sendQuery(ctx context.Context, noResponseErrCh chan<- e
 				noResponseErrCh <- err
 				return
 			}
-			var length int16
+			var length uint16
 			err = binary.Read(bytes.NewReader(respBuf.Bytes()), binary.BigEndian, &length)
 			if err != nil {
 				errors.LogErrorInner(ctx, err, "failed to parse response length")

app/dns/nameserver_tcp.go

@@ -173,7 +173,7 @@ func (s *TCPNameServer) sendQuery(ctx context.Context, noResponseErrCh chan<- er
 				noResponseErrCh <- err
 				return
 			}
-			var length int16
+			var length uint16
 			err = binary.Read(bytes.NewReader(respBuf.Bytes()), binary.BigEndian, &length)
 			if err != nil {
 				errors.LogErrorInner(ctx, err, "failed to parse response length")