Currently, when we add iptables rules, we keep them on a list so that
we can easily reload them on e.g. 'service libvirtd reload'.

However, we don't save this list to disk, so if libvirtd is restarted
we lose the ability to reload the rules.

The fix is simple - just re-add the damn things on reload.

Note, we delete the rules before re-adding them, just like the current
behaviour of iptRulesReload().

* src/network/bridge_driver.c: re-add the iptables rules on reload.