iptables: correct invalid syntax in nat table
    
    This `[0:]` syntax doesn't seem to be correct. iptables 1.8.10
    errors out on encountering it, saying:
    
    invalid policy counters for chain 'PREROUTING'
    
    this seems to be because the check was tightened between 1.8.9
    and 1.8.10 to apply even when iptables is not actively restoring
    the counters:
    https://git.netfilter.org/iptables/commit/?id=4a2b2008fdf4df980433f99a6d8f2003f2005296
    
    I think these are all meant to be 0:0, so let's make them that
    and stop iptables choking.
    
    Signed-off-by: Adam Williamson <awilliam@redhat.com>