libbpf: Use local includes inside the library

In our monrepo, we try to minimize special processing when importing
(aka vendor) third-party source code. Ideally, we try to import
directly from the repositories with the code without changing it, we
try to stick to the source code dependency instead of the artifact
dependency. In the current situation, a patch has to be made for
libbpf to fix the includes in bpf headers so that they work directly
from libbpf/src.

Signed-off-by: Sergey Kacheev <s.kacheev@gmail.com>
Acked-by: Yonghong Song <yonghong.song@linux.dev>
Link: https://lore.kernel.org/r/CAJVhQqUg6OKq6CpVJP5ng04Dg+z=igevPpmuxTqhsR3dKvd9+Q@mail.gmail.com


Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>