Fix matching pong in ping_pong app

Author: pablogs9

apps/ping_pong/app.c

@@ -51,8 +51,9 @@ void appMain(void *argument)
   rcl_publisher_t pong_publisher = rcl_get_zero_initialized_publisher();
   rcl_publisher_init(&pong_publisher, &node, ROSIDL_GET_MSG_TYPE_SUPPORT(std_msgs, msg, Header), "/microROS/pong", &pong_publisher_ops);
 
-  // Create a reliable pong subscriber
+  // Create a best effort pong subscriber
   rcl_subscription_options_t pong_subscription_ops = rcl_subscription_get_default_options();
+  pong_subscription_ops.qos.reliability = RMW_QOS_POLICY_RELIABILITY_BEST_EFFORT;
   rcl_subscription_t pong_subscription = rcl_get_zero_initialized_subscription();
   rcl_subscription_init(&pong_subscription, &node, ROSIDL_GET_MSG_TYPE_SUPPORT(std_msgs, msg, Header), "/microROS/pong", &pong_subscription_ops);