Only check for flow label functionality in the QUIC end-to-end test
if the connection is actually using IPv6.

Will unbreak QUICHE Chromium merge.

PiperOrigin-RevId: 686934343

quiche/quic/core/http/end_to_end_test.cc

diff --git a/quiche/quic/core/http/end_to_end_test.cc b/quiche/quic/core/http/end_to_end_test.cc
index 325ace9..6172baa 100644
--- a/quiche/quic/core/http/end_to_end_test.cc
+++ b/quiche/quic/core/http/end_to_end_test.cc
@@ -7764,13 +7764,15 @@
 
   client_->SendSynchronousRequest("/foo");
 
-  EXPECT_EQ(client_flow_label, client_connection->outgoing_flow_label());
-  EXPECT_EQ(server_flow_label, client_connection->last_received_flow_label());
+  if (server_address_.host().IsIPv6()) {
+    EXPECT_EQ(client_flow_label, client_connection->outgoing_flow_label());
+    EXPECT_EQ(server_flow_label, client_connection->last_received_flow_label());
 
-  server_thread_->Pause();
-  QuicConnection* server_connection = GetServerConnection();
-  EXPECT_EQ(server_flow_label, server_connection->outgoing_flow_label());
-  EXPECT_EQ(client_flow_label, server_connection->last_received_flow_label());
+    server_thread_->Pause();
+    QuicConnection* server_connection = GetServerConnection();
+    EXPECT_EQ(server_flow_label, server_connection->outgoing_flow_label());
+    EXPECT_EQ(client_flow_label, server_connection->last_received_flow_label());
+  }
 }
 
 TEST_P(EndToEndTest, ServerReportsNotEct) {