I've checked your new code. It is correct behaviour that you can't connect
with your client. If Linux lets you to do it, Linux must be fixed. RFC
2373 part 2.5.2 says the following :

   The unspecified address must not be used as the destination address
   of IPv6 packets or in IPv6 Routing Headers.

What you need to do is the same thing that for ipv4. You need to know
one of the adress of the host you want to join (localhost here). For
that purpose, you need to call getaddrinfo and look for AF_INET6 adress
(man getaddrinfo has some nice examples). With this adress, you can
connect to your server.

I hope it will help you.

Regards,
-- 
Arnaud Degroote
degroote@netbsd.org