peer: eliminate circular waiting by calling maybeSendNodeAnn async

In this commit, we attempt to fix circular waiting scenario introduced
inadvertently when [fixing a race condition
scenario](lightningnetwork#7856). With that
PR, we added a new channel that would block `Disconnect`, and
`WaitForDisconnect` to ensure that only until the `Start` method has
finished would those calls be allowed to succeed.

The issue is that if the server is trying to disconnect a peer due to a
concurrent connection, but `Start` is blocked on `maybeSendNodeAnn`,
which then wants to grab the main server mutex, then `Start` can never
exit, which causes `startReady` to never be closed, which then causes
the server to be blocked.

This PR attempts to fix the issue by calling `maybeSendNodeAnn` in a
goroutine, so it can grab the server mutex and not block the `Start`
method.

Fixes lightningnetwork#7924

Fixes lightningnetwork#7928

Fixes lightningnetwork#7866

peer/brontide.go

@@ -672,7 +672,7 @@ func (p *Brontide) Start() error {
 	//
 	// TODO(wilmer): Remove this once we're able to query for node
 	// announcements through their timestamps.
-	p.maybeSendNodeAnn(activeChans)
+	go p.maybeSendNodeAnn(activeChans)
 
 	return nil
 }