bpf: sockmap test script

This adds the test script I am currently using to validate
the latest sockmap changes. Shortly sockmap will be ported
to selftests and these will be run from the infrastructure
there. Until then add the script here so we have a coverage
checklist when porting into selftests.

Signed-off-by: John Fastabend <john.fastabend@gmail.com>
Acked-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>