bpf: add missing entries to bpf_helpers.h

This header defines the BPF functions enumerated in uapi/linux.bpf.h
in a callable format. Expand to include all registered functions.

Signed-off-by: Willem de Bruijn <willemb@google.com>
Acked-by: Song Liu <songliubraving@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>