[PATCH wireguard] wireguard: selftests: refactor the test structure

[Jason A. Donenfeld]

Hi Hangbin,

I don't know how interested in this I am. Splitting things into two
files means more confusing maintenance, and categorizing sections
strictly into functions means there's more overhead when adding tests
(e.g. "where do they fit?"), because the categories you've chosen are
fairly broad, rather than being functions for each specific test. I'd
be more amenable to something _entirely_ granular, because that'd be
consistent, or what we have now, which is just linear. Full
granularity, though, has its own downsides, of increased clutter.
Alternatively, if you'd like to add some comments around the different
areas to better document what's happening, perhaps that'd accomplish
the same thing as this patch.

Jason