einwilligung-hcp

As reported in [0], we are missing openat2.h in libbpf-local UAPI
headers. Sync it and adjust sync script to keep syncing it going
forward.

  [0] https://github.com/libbpf/libbpf/issues/649

Closes: https://github.com/libbpf/libbpf/issues/649


Signed-off-by: Andrii Nakryiko <andrii@kernel.org>