Use correct macro

src/core/ext/transport/chttp2/server/chttp2_server.cc

@@ -366,7 +366,7 @@ grpc_error* grpc_chttp2_server_add_port(grpc_server* server, const char* addr,
   grpc_resolved_addresses_destroy(resolved);
 
   arg = grpc_channel_args_find(args, GRPC_ARG_ENABLE_CHANNELZ);
-  if (grpc_channel_arg_get_bool(arg, false)) {
+  if (grpc_channel_arg_get_bool(arg, GRPC_ENABLE_CHANNELZ_DEFAULT)) {
     state->channelz_listen_socket =
         grpc_core::MakeRefCounted<grpc_core::channelz::ListenSocketNode>(
             grpc_core::UniquePtr<char>(gpr_strdup(addr)));