cord/ep: enable THREAD_CREATE_STACKTEST for thread

sys/net/application_layer/cord/ep/cord_ep_standalone.c

@@ -87,7 +87,8 @@ static void *_reg_runner(void *arg)
 
 void cord_ep_standalone_run(void)
 {
-    thread_create(_stack, sizeof(_stack), PRIO, 0, _reg_runner, NULL, TNAME);
+    thread_create(_stack, sizeof(_stack), PRIO, THREAD_CREATE_STACKTEST,
+                  _reg_runner, NULL, TNAME);
 }
 
 void cord_ep_standalone_signal(bool connected)