Session config: set scouting/multicast/autoconnect_strategy/peer/to_peer=always

[JEnoch]

As explained in eclipse-zenoh/zenoh#1890, the combination of multicast scouting and autoconnect_strategy=greater_zid can lead to peer-to-peer connection establishment to take up to 8 seconds.

This causes issues in tests when configured with multicast, but could also cause timeout issues at launch time for users who want to use multicast scouting. Waiting for eclipse-zenoh/zenoh#1890 to be fixed, I think it's preferable to set scouting/multicast/autoconnect_strategy/peer/to_peer=always in DEFAULT_RMW_ZENOH_SESSION_CONFIG.json5.

This will fix #596 and possibly other tests when running with multicast scouting enabled.
But it won't change the current default behaviour for users relying on a router and gossip scouting.

[ahcorde]

Pulls: #604
Gist: https://gist.githubusercontent.com/ahcorde/8b24ac1110170a0c67b6f12438056c15/raw/7d3efb25e1c9bfd8fc89f162e7dae0026ee1a6ea/ros2.repos
BUILD args: --packages-above-and-dependencies rmw_zenoh_cpp
TEST args: --packages-above rmw_zenoh_cpp
ROS Distro: rolling
Job: ci_launcher
ci_launcher ran: https://ci.ros2.org/job/ci_launcher/15620

• Linux
• Linux-aarch64
• Linux-rhel
• Windows

[Yadunund]

Converting to draft as this PR seems to address an issue with multicast scouting which we plan to move away from in our CI jobs.

Given that the RMW freeze is today, i'm inclined to pause on merging this in.

If we get reports of "bugs" caused by this behavior, we can always merge it in after the feeze as a bug fix but I'm hoping the router will be running in our CI jobs by then.

Unless it's preferable to set scouting/multicast/autoconnect_strategy/peer/to_peer=always even with the router?

[JEnoch]

Unless it's preferable to set scouting/multicast/autoconnect_strategy/peer/to_peer=always even with the router?

I think it's pointless since the peers are configured to connect at startup to the router on tcp/localhost:7447, without scouting and thus without delay.

[Yadunund]

Closing this one out for reasons described above.