Previously, receiving labeled responses to messages sent from a
downstream without echo-message would fail, because soju would filter
out the responses under the assumption that it was an echoed message.
Only do this filtering when msg.Prefix.Name != uc.nick in order to avoid
Hm, I think this breaks if upstream sends a message which isn't echo
but still is our own prefix. This can happen if another client is
connected to the upstream server with the same nick, or if the server
is configured with an auto-reply of some kind, etc.