Expose Error Types of Relay and DCUtR

[canewsin]

This Exposure is required for passing swarm event to handler methods, instead dealing them at one place.

event = swarm1.select_next_some() => {
      match event {
                 event =>  DecentNetworkBehaviour::handle_swarm_event(&mut swarm1, event, &client_config1)
     }
}

[mxinden]

Thanks for the patch. One comment. Also missing changelog entries in protocols/dcutr/changelog.md and protocols/relay/changelog.md.

[canewsin]

Thanks for the patch. One comment. Also missing changelog entries in protocols/dcutr/changelog.md and protocols/relay/changelog.md.

@mxinden
Should I add change log under unreleased versions for each protocol?

[mxinden]

Should I add change log under unreleased versions for each protocol?

Yes please. See https://github.com/libp2p/rust-libp2p/blob/master/docs/release.md

[canewsin]

@mxinden 👍

[mxinden]

Merged via #2605. Thanks @canewsin!