Support bpf_xdp_attach and bpf_xdp_detach

[insearchoflosttime]

Defined in libbpf as:

LIBBPF_API int bpf_xdp_attach(int ifindex, int prog_fd, __u32 flags,
			      const struct bpf_xdp_attach_opts *opts);
LIBBPF_API int bpf_xdp_detach(int ifindex, __u32 flags,
			      const struct bpf_xdp_attach_opts *opts);

https://github.com/libbpf/libbpf/blob/3591deb9bc6b0848721f831790b78ae0a593b4c5/src/libbpf.h#L898-L901