Fix build problem in test.

test/core/end2end/fixtures/h2_ssl_cert.c

@@ -267,7 +267,7 @@ static grpc_end2end_test_fixture begin_test(grpc_end2end_test_config config,
   gpr_log(GPR_INFO, "%s/%s", test_name, config.name);
   f = config.create_fixture(client_args, server_args);
   config.init_server(&f, server_args);
-  config.init_client(&f, client_args);
+  config.init_client(&f, client_args, NULL);
   return f;
 }