augment quic demos to support ipv4/6 connections

augment quic demos to support ipv4/6 connections

Because the quicserver utility supports expressly listening in ipv4/6
mode, its possible/likely that the server will listen on an ipv4
address, while the clients will connect via ipv6, leading to connection
failures.

Augment quic demo clients to afford them the same -6 option that the
server has so that connection family can be co-ordinated

Reviewed-by: Nicola Tuveri <nic.tuv@gmail.com>
Reviewed-by: Hugo Landau <hlandau@openssl.org>
Reviewed-by: Matt Caswell <matt@openssl.org>
Reviewed-by: Richard Levitte <levitte@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/22577)