libbpf v0.3

New features/APIs:

• kernel modules BTF support on all levels;
• ring_buffer__epoll_fd() API;
• xsk_socket__update_xskmap() and xsk_setup_xdp_prog() APIs.

New BPF helpers:

• bpf_task_storage_get() and bpf_task_storage_delete();
• get_current_task_btf();
• bpf_bprm_opts_set();
• bpf_ktime_get_coarse_ns();
• bpf_ima_inode_hash();
• bpf_sock_from_file().

Bug fixes:

• ring_buffer__poll() returns number of consumed records correctly;
• handle corner-case case with unused sub-programs;
• xsk_socket__delete() bug fixes.