Adds the following to codegen:
- `bpf_cgroup_iter_order`: used in `bpf_link_info.iter.group.order`
- `NFPROTO_*`: used in `bpf_link_info.netfilter.pf`
- `nf_inet_hooks`: used in `bpf_link_info.netfilter.hooknum`
Include `linux/netfilter.h` in `linux_wrapper.h` for `NFPROTO_*` and
`nf_inet_hooks` to generate.
Aya::obj depends on bindgen generated files, and we start
by migrating bindgen generated files.
This commit adds the new aya-obj crate to the workplace
and migrates generated files into the crate. We use core
instead of std in an effort to make the final crate no_std.
Bindgen was run against libbpf v1.0.1.
Refs: #473