Would be nice to add CIDR notation to this, but this is the minimal
thing needed for the security fix.
This commit was sponsored by Ewen McNeill on Patreon.
For use in a security boundary enforcement.
Based on https://en.wikipedia.org/wiki/Reserved_IP_addresses
Including supporting IPv4 addresses embedded in IPv6 addresses. Because
while RFC6052 3.1 says "Address translators MUST NOT translate packets
in which an address is composed of the Well-Known Prefix and a non-
global IPv4 address; they MUST drop these packets", I don't want to
trust that implementations get that right when enforcing a security
boundary.
This commit was sponsored by John Pellman on Patreon.
