Use family when saving iptables rule.

Will save ipv6 rules to proper file.
Allow name argument for pknock iptables module.
Merge pull request #11849 from zeezooz/iptables_save_family

Use family when saving iptables rule.
Merge pull request #11850 from zeezooz/iptables_pknock_name

Allow name argument for pknock iptables module.
The returned value can also be `None`