ncm-iptables: Negation syntax has changed upstream

[jrha]

This snippet:

'filter/rules' = merge(SELF, list(
    dict(
        'command', '-A',
        'chain', 'FORWARD',
        'src_addr', '! 8.8.8.8',
        'jump', 'DROP',
    ),
);

Generates the following iptables line:

-A FORWARD -s ! 8.8.8.8 -j DROP

This syntax for negation was deprecated and removed at some point in the past, it should generate:

-A FORWARD ! -s 8.8.8.8 -j DROP

It might not be worth fixing this given that we should probably be putting development effort into supporting something other than iptables, so maybe the best option is to change the documentation to state that this is no longer supported.