Add note to keep prefer_quic_client_udp_gro flag

Signed-off-by: Yan Avlasov <yavlasov@google.com>

source/common/runtime/runtime_features.cc

@@ -77,6 +77,8 @@ RUNTIME_GUARD(envoy_reloadable_features_oauth_make_token_cookie_httponly);
 RUNTIME_GUARD(envoy_reloadable_features_oauth_use_standard_max_age_value);
 RUNTIME_GUARD(envoy_reloadable_features_oauth_use_url_encoding);
 RUNTIME_GUARD(envoy_reloadable_features_original_dst_rely_on_idle_timeout);
+// Ignore the automated "remove this flag" issue. UDP GRO can cause noticeable performance
+// regression. This flag may need to be moved into configuration or kept indefinitely.
 RUNTIME_GUARD(envoy_reloadable_features_prefer_quic_client_udp_gro);
 RUNTIME_GUARD(envoy_reloadable_features_proxy_status_mapping_more_core_response_flags);
 RUNTIME_GUARD(envoy_reloadable_features_proxy_status_upstream_request_timeout);