lib/net: `Request_Handler` should be `Connection_Handler`

[maxteufel]

it does not make sense to talk about "requests" at this layer of the network stack

[michaellilltokiwa]

Also channel should probably be renamed to e.g. connection?

[maxteufel]

I'm not sure about renaming channel to connection. That would kinda imply being able to call something like connection.close which isn't what channel currently handles. Open to better suggestions though.

[michaellilltokiwa]

fixed by #3513