Re: [libvirt] [PATCHv2 05/13] Pass prefix rather than netmask into iptables functions

IPv6 will use prefix exclusively, and IPv4 will also optionally be able to use it, and the iptables functions really need a prefix anyway, so use the new virNetworkDefPrefix() function to send prefixes into iptables functions instead of netmasks. Also, in a couple places where a netmask is actually needed, use the new private API function for it rather than getting it directly. This will allow for cases where no netmask or prefix is specified (it returns the default for the current class of network.)