net_sched: act_ipt forward compat with xtables

[ Upstream commit 0dcffd09641f3abb21ac5cabc61542ab289d1a3c ]

Deal with changes in newer xtables while maintaining backward
compatibility. Thanks to Jan Engelhardt for suggestions.

Signed-off-by: Jamal Hadi Salim <jhs@mojatatu.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>