Notifications are racy

[Stebalien]

We notify in parallel (per notification). This means that anything trying to tag connections before the connection manager finishes registering the connection will fail.

One way to fix this is to add an IsConnected method to connections (would be nice to have anyways and we generally have this at lower levels) and start tracking active connections before we actually receive a notification.

Thoughts @whyrusleeping?

[Stebalien]

Related to ipfs/kubo#4353.

[Stebalien]

Actually, the "IsConnected" method won't help. However, the conn manager will need access to the swarm (which it doesn't currently have).