Fixes #3021, #5246

This means ConnectionPEP now knows the objects on which it calls method. Before, it just assumed that: "it will be subclassed and that the subclass defines a few methods".

Big advantage is that false positives in the pylint report are gone

This makes it easier to reason about its usage.

This prevents dialogs poping up with showing "Service unavailable".

Sorry for not disclosing my real name to the wide audience. I'm just
that paranoid...

we can now send pep thing to a zeroconf connection objec, it will just send nothing. so GUI doesn't have to know it's a zeroconf connection or not. fixes #5432