Epollcat can now use Scala Native IPv6 detection

[LeeTibbert]

Now that Epollcat requires Scala Native 4.9, I think that Epollcat's IPv6 detection
could be simplified by using Scala Native's IPv6 detection. That code is, I believe,
in Scala Native 4.9.

There is an adage about letting sleeping dogs lie, and the current code seems
to be working, so this is, IMO, not the highest priority.

I note is so that I do not forget "hanging chads"/undone_promises. The
main reason is to simplify the epollcat network handling.