Debian Packaging work for WireGuard:

 * wireguard metapackage should accept a 5.6 (or later) kernel instead
   of a module

 * consider make check for wg during build: this depends on
   scan-build, which is part of clang, but also wants to clean the
   build tree first.  Currently, we don't do any build-time tests.

 * autopkgtest:

  - from src/, run "make check" (depending on clang-tools and sparse)
    and make sure it looks plausible.

  - Can we add other tests?