adding bpf's sample program which is using bpf_xdp_adjust_tail helper
by generating ICMPv4 "packet to big" message if ingress packet's size is
bigger then 600 bytes
Signed-off-by: NNikita V. Shirokov <tehnerd@tehnerd.com>
Signed-off-by: NDaniel Borkmann <daniel@iogearbox.net>