TLSProxy::Proxy: If we don't support IPv6, force IPv4

We use the first we can of the following IO::Socket modules to create
sockets:

- IO::Socket::INET6
- IO::Socket::IP
- IO::Socket::INET

The last of them doesn't support IPv6, so if that's the one available,
we must force the s_client and s_server processes to use IPv4.

Reviewed-by: Bernd Edlinger <bernd.edlinger@hotmail.de>
(Merged from https://github.com/openssl/openssl/pull/5092)