ContainsIPv4Loopback() claimed that "::/0" contains IPv4 loopback IPs
(on the theory that listening on "::/0" will listen on "0.0.0.0/0" as
well and thus include IPv4 loopback). But its sole caller (the
iptables proxier) doesn't use listen() to accept connections, so this
theory was completely mistaken; if you passed, eg,
`--nodeport-addresses 192.168.0.0/0,::/0`, then it would not create
any rule that accepted nodeport connections on 127.0.0.1, but it would
nonetheless end up setting route_localnet=1 because
ContainsIPv4Loopback() claimed it needed to. Fix this.
Add names to the tests and use t.Run() (rather than having them just
be numbered, with number 9 mistakenly being used twice thus throwing
off all the later numbers...)
Remove unnecessary FakeNetwork element from the testCases struct since
it's always the same. Remove the expectedErr value since a non-nil
error is expected if and only if the returned set is nil, and there's
no reason to test the exact text of the error message.
Fix weird IPv6 subnet sizes.
Change the dual-stack tests to (a) actually have dual-stack interface
addrs, and (b) use a routable IPv6 address, not just localhost (given
that we never actually want to use IPv6 localhost for nodeports).
