Add ipv6 attribute respect to Ubuntu iptables
Add ipv6 attribute respect to Ubuntu iptables

- Don't write rules.v6 on ubuntu if `node['firewall']['ipv6_enabled']` is disabled

chef-cookbooks/firewall,williamsjj/firewall,opscode-cookbooks/firewall,williamsjj/firewall,chef-cookbooks/firewall,opscode-cookbooks/firewall