When installing libbpf headers into 'lib/libbpf/src/root/' then the git
submodule for libbpf is marked dirty. This result in stgit complains under
different operations.
This patch fix the issue by installing libbpf outside submodule directory.
Choose directory 'lib/libbpf-install/' to emphasize relation to 'lib/libbpf/'.
V2: Don't install the library only the header files as before. Also
installing the should be a separate commit. Patch still statically
link with libbpf/src/libbpf.a.
Signed-off-by: Jesper Dangaard Brouer <netoptimizer@brouer.com>
