Re-use the main filter node for the tf2_ros::MessageFilter TransformListener

[Hugal31]

The TransformListener recommends to re-use a node when possible.

This avoids spawning a new node uselessly.

By the way, I think we could also pass spin_thread=false in this specific use case, since we don't use the timeout mechanism.

[jonbinney]

Interesting.... in the old code, after launching, do you see the extra node running (e.g. with ros2 node list)?

[Hugal31]

Yes

> ros2 run laser_filters scan_to_scan_filter_chain --ros-args -p tf_message_filter_target_frame:=foobar &
> ros2 node list
/scan_to_cloud_filter_chain
/transform_listener_impl_63ec3974c7c0

[jonbinney]

Looks good!