Add libbpf0, libbpf-dev packages (#914428)

Even if bpftool cannot be distributed at the moment due to GPL2/GPL3 licensing issues (!72 (closed)), it would still be useful to ship libbpf which is LGPL2+-licensed and thus has no obvious licensing problems.

Included is a patch that adds a SONAME to the shared library.

AFAICS there is no need to limit the architectures on which the library is built.