Revert "Revert "Move createChildChains to iptables-restore.""

This reverts commit f81cda0e.

Reason for revert: it should be safe to roll forward again
because the next CL in this change stack removes the root cause
of the boot failure.

Test: bullhead builts, boots
Test: netd_{unit,integration}_test pass
Bug: 32323979
Change-Id: Idb462d691d66e00b6ce806aa69582ecdbc930faf