C0103 fixes 3, dht, k_bucket and routing_table

This PR is dependent on #1108.
I tried to not change the structure of `msg`. I had the impression that this is part of the outward facing interface. For instance on line 167 it says `new_peer.send(response_msg)`. If I would change `msg`, the code on the receiving end has to be changed as well. Not sure how to do that.
I suggest, I change back line 758? I think that was an erroneous change.