Net: Allow to exclude this functionality at compile time

[solardiz]

Nov 28, 2022

This is now implemented as LKRG_WITH_NET defined in net.h.

I suggest we use the LKRG_WITH_* naming for these things, and we might later move them all e.g. to a config.h file.

While at it, I found that disabling of our P_LKRG_UNHIDE (to be renamed to LKRG_WITH_UNHIDE later) does something weird: #251

[solardiz]

The remaining task here, if any, may be to wrap or move this setting into a documented make command-line knob or into a new config.h file. We could also reconsider the default - having this compiled in was good during development at least to get more testing from GitHub Actions, but do we want this included in most LKRG builds or not?