Force use of IPv4 for LDAP test.

[puck]

Net::LDAP::Server::Test binds to IPv6 by default if IPv6 is enabled, but Net::LDAP uses 'localhost' which resolves to an IPv4 address. Even when I switched the call to Net::LDAP->new() to use ip6-localhost it failed elsewhere due to RT using 127.0.0.1.