Revert "Move createChildChains to iptables-restore."

This reverts commit 81ff64ec.

Reason for revert: botloops ryu. Incomplete error handling code
in IptablesRestoreController interacts badly with an iptables
error early on caused by ryu not having the iptables "nat" table.

Test: builds, boots bullhead
Test: fixes ryu bootloop
Fix: 35027505
Change-Id: I209c74e46cfcdb80ca2c3e0e6ce9c28f389017ec