Use iptables-restore to set the incoming packet mark rule.

This speeds up network switching because one rule needs to be
added/removed per interface.

Bug: 28362720
Test: bullhead builds, boots
Test: netd_{unit,integration}_test pass
Test: watch -n1 "adb shell iptables -v -n -t mangle -L INPUT" while switching networks
Change-Id: Ie536db6a50d018c88bb03c5f069965e99e0d162e