Fix iptables dport and sport

Just wrapping the relevant vars / spots with str() where necessary - recent code additions/changes assume kwargs['sport'] and kwargs['dport'] (also sports and dports) are strings... I was getting exceptions though, seems they're being converted to ints before hitting this code (at least some of the time, ie: likely depends on actual yaml value in question). Anyways, this small fix solves the issue for me locally, I believe it's correct and also pinged the original author of the lines in question and got stamp of approval for this mod.

Let me know if there's any issue with this/etc, otherwise... enjoy :)