#4 make gss work between ipv6 server and ipv4 client

[Tomas Klacko]

When proftpd listens for clients on IPv6 address which is a mapped IPv4 address
and channel bindings are enabled then IPv4 clients will be denied connection.
This happens because the client uses IPv4 bindings and server uses IPv6 bindings.
In this particular case, the change makes use of IPv4 bindings on the server
instead of IPv6 ones.

[Tomas Klacko]

changes to mod_gss.c.in

[Markus Moeller]

I'll check and commit if good