samples/bpf: Add option to dump socket settings

Add option to dump socket settings. Will be used in the next patch
to verify bpf programs are correctly setting mark, priority and
device based on the cgroup attachment for the program run.

Signed-off-by: David Ahern <dsahern@gmail.com>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>