Relay doesn't seem to work with a discovery server #145

Description

Something seems to break when trying to use a relay topic with a discovery server, and the relay never gets established.

To Reproduce

1. Run fastdds discovery --server-id 0 -l 127.0.0.1 -p 14520
2. In a new terminal, export ROS_DISCOVERY_SERVER=127.0.0.1:14520; ros2 daemon stop; ros2 daemon start
3. Run ros2 launch broken_discovery_example_launch.yaml (below). The nonrelay_listener will hear the messages coming through but the relay_listener never hears anything.
4. Kill that launch and run unset ROS_DISCOVERY_SERVER; ros2 daemon stop; ros2 daemon start.
5. Run ros2 launch broken_discovery_example_launch.yaml. Both listeners hear the messages coming through.

System

• OS: Ubuntu 22.04
• ROS 2 Distro: Jazzy

Contents of broken_discovery_example_launch.yaml:

---
launch:
- node:
    pkg: demo_nodes_cpp
    exec: talker
- node:
    pkg: demo_nodes_py
    exec: listener
    name: nonrelay_listener
- node:
    pkg: demo_nodes_py
    exec: listener
    name: relay_listener
    remap:
      - from: chatter
        to: chatter_relay
- node:
    pkg: topic_tools
    exec: relay
    output: screen
    param:
      - name: input_topic
        value: chatter
      - name: output_topic
        value: chatter_relay