MINOR: tools: add is_ip_untrusted() to check for non-local addresses

MINOR: tools: add is_ip_untrusted() to check for non-local addresses

The function will return true for non-local ipv4/ipv6 addresses only.
Some are between the two (benchmark, doc, examples, cgn etc) and are
intentionally reported as non-local hence untrusted as well, the
rationale being that they're normally not deployed for production so
they shouldn't be taken for trusted local addresses. This will be
used in future commits.