CMake, BSD: Fix BPF detection, use clonable device

[klemensn]

• CMake: Typofix BSD bpf guard
• BSD: bpf(4) is clonable, use /dev/bpf
• CMake: Fix net/bpf.h detection on OpenBSD
• CMake: BSD: Fix bpf detection
• CMake: Linux: Pick BPF last

[klemensn]

There's more to fix in the CMake code and it makes sense to have it in one PR, so converting it to a draft until I have everything...

[klemensn]

This gets src/eth-bsd.c to be used instead of src/eth-none.c on OpenBSD, as expected. Linux should still pick src/eth-linux.c, but I haven't built there.

/dev/tun0 detection is equally broken and can use the same fix, but that should be another PR.

[ofalk]

Awesome @klemensn - happy someone is looking into the BSD part, because I have none to my avail at the moment ! May I consider this read to be merged?

[klemensn]

Awesome @klemensn - happy someone is looking into the BSD part, because I have none to my avail at the moment ! May I consider this read to be merged?

Your call -- if this looks good enough, I'll fix other CMake stuff as well until OpenBSD is happy enough that I can consider switching upgrading our official net/libdnet port/package and switch it over to from GNU auto* tooling.

Works (better) for me, I don't see how this would make it worse for any other system...

[ofalk]

Awesome @klemensn - happy someone is looking into the BSD part, because I have none to my avail at the moment ! May I consider this read to be merged?

Your call -- if this looks good enough, I'll fix other CMake stuff as well until OpenBSD is happy enough that I can consider switching upgrading our official net/libdnet port/package and switch it over to from GNU auto* tooling.

Works (better) for me, I don't see how this would make it worse for any other system...

Builds fine on Linux and it looks fine. I'll merge it in a sec - this time as merge commit - not squash it :-)