fix(dht): Self-connection guards in DhtNode

[teogeb]

When we receive connection event from transport, we have been checking if the connection is from this node. We check that fact both when we receive connected event from ITransport, and when we query the initial connections.

If the connection is from this node we now return from the methods and don't update the connections state.

This is a cherry-pick from #1803, i.e. the original author is @ptesavol.

Open question

• Is the error state possible in practice? If we receive a connection from self, is that a bug? (In that case we should fix the bug and could ignore this PR. We could also remove the related error logging.)

[ptesavol]

LGTM