Importing libraries for the kernel

[Ryota Ozaki <ozaki-r%netbsd.org@localhost>]

Hi,

As you may know I'm working on implementing WireGuard
in the kernel.  The implementation works and buildable.
Some code cleanups are still needed but I'll propose it on
the list in the near future.

Before that, I want to ask about how to import cryptography
libraries needed tor the implementation.  The libraries are
libb2[1] and libsodium[2]: the former is for blake2s and
the latter is for curve25519 and [x]chacha20-poly1305.

[1] https://github.com/BLAKE2/libb2
[2] https://github.com/jedisct1/libsodium

Both libraries are not BSD (CC0 and ISC) and so I imported
them into sys/external/, added some gules for build and
copied some header files in sys/crypto/ to include them
from kernel codes.

I can build normal kernels and rump kernels with the libraries,
but the way of importing the libraries is a bit awkward.  It would
be clean if directly import them into sys/crypto/, but I'm not sure
if it's acceptable.  blake2s might be okay because it's CC0
which is a kind of public domain, IIUC.

The diff includes glue codes of the library import in question:
  http://www.netbsd.org/~ozaki-r/import-libs.diff

Any suggestions?

Thanks,
  ozaki-r