libbpf: add function to setup XDP

Most of the code is taken from set_link_xdp_fd() in bpf_load.c and
slightly modified to be library compliant.

Signed-off-by: Eric Leblond <eric@regit.org>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
3 files changed