iptable child chains are disabled by default. Ignore the initial disable request so netd won't throw errors when it cannot detach chains that do not exist. Bug: 22800189 Change-Id: I70b4b8b9e6a5dbffe32841941922b7fd92dcd3d6 Original-Change-Id: I9312dd558ba6d59dc6aa394afeb66a222daafcf9 [cernekee: backported from master branch]