The micro_ros_agent does not relay topic messages

使用 galactic micro-ROS Agent Docker 命令、teleop_twist_keyboard，以及 micro_ros_subscriber_twist.ino 和 micro_ros_publisher.ino 範例，重現兩種順序情境。先比較 MCU 程式在發佈前啟動與在發佈後啟動時 agent 的行為和 logs；當預期訊息在兩個已記錄的情境中都能可靠傳遞，或預期限制已清楚記錄時，即視為完成。

Describe the bug

Hi, I tried this example micro-ros_subscriber_twist using UDP on STM32F407 (Ethernet), but the micro_ros_agent only relays the message to MCU if

[Normal]
Step 1: Start the agent
Step 2: Start the program on MCU
Step 3: Publish the twist message (keep publishing)

Twist messages received.

If I exchange step 2 with step 3, I cannot receive the message on MCU:

[BUG]
Step 1: Start the agent
Step 2: Publish the twist message (keep publishing)
Step 3: Start the program on MCU

No Twist messages.

I'm wondering is this an expected behavior or a BUG?

Besides, the micro-ros_publisher.ino example cannot receive the int32 message under both scenarios.

To Reproduce

Scenario 1 (BUG):

$ Step 1: Start the agent
$ docker run -it -p 9999:9999/udp --privileged microros/micro-ros-agent:galactic udp4 -p 9999 -v 6

$ Step 2: Publish the twist message
$ docker container -it sleepy_rubin /bin/bash
$ # Inside the container
$ ros2 run teleop_twist_keyboard teleop_twist_keyboard 

$ Step 3: Start the program on MCU
$ micro_ros_sub twist

# No twist message on MCU

Scenario 1 (Normal):

$ Step 1: Start the agent
$ docker run -it -p 9999:9999/udp --privileged microros/micro-ros-agent:galactic udp4 -p 9999 -v 6

$ Step 2: Start the program on MCU
$ micro_ros_sub twist

$ Step 3: Publish the twist message
$ docker container -it sleepy_rubin /bin/bash
$ # Inside the container
$ ros2 run teleop_twist_keyboard teleop_twist_keyboard 

# Normal twist message on MCU