Attempts to delete the specified user-defined chain (all the
        chains in the table if none is given).

def delete_chain(self, chainname=None):
        """Attempts to delete the specified user-defined chain (all the
        chains in the table if none is given).
        """
        args = ['-X']
        if chainname: args.append(chainname)
        self.__run_iptables(args)