io: preserve ipv4/ipv6 flags when resolving InetSocketAddress

io: preserve ipv4/ipv6 flags when resolving InetSocketAddress

The original InetSocketAddress struct may have has_ipv4 and
has_ipv6 fields set, which will control both the ai_family
used during DNS resolution, and later use of the V6ONLY
flag.

Currently the standalone DNS resolver code drops the
has_ipv4 & has_ipv6 flags after resolving, which means
the later bind() code won't correctly set V6ONLY.

This fixes the following scenarios

  -vnc :0,ipv4=off
  -vnc :0,ipv6=on
  -vnc :::0,ipv4=off
  -vnc :::0,ipv6=on

which all mistakenly accepted IPv4 clients

Acked-by: Gerd Hoffmann <kraxel@gmail.com>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>