tracer: several events logged before connection_started

[marten-seemann]

For example: congestion_state_updated, key_updated, version_information

There's nothing inherently wrong with that, but it would be nicer if connection_started was the very first thing that happens on a new connection.

[marten-seemann]

The problem here is that we only emit the connection_started once we've actually decrypted the first Initial packet. Otherwise, we might log a corrupted source connection ID (and we only find this out after applying the AEAD). This means that all the code paths that log on initialization will log before that.