DO NOT MERGE: Update OEM iptable hooks and ip fwd

This is a squash of two changes from partner repo:

    Clean up OEM iptables hooks

    Id: Ife7a1c08ca88beba2dede776d2e4dd6097dad05a

And

    Add hooks for OEM iptables rules and IP fwd

    - Useful for integrating peripherals that use IP for control and
    diagnostics.
    - Add hooks for specifying static iptables rules at startup.
    - Add system prop to keep IP forwarding enabled all the time.
    - Remove the ro.bootmode=bp-tools hacks.

    Id: Ic70d4c88179c530414505976193bf616037500a6

Bug: 5045218
Change-Id: I4229d3576426880b68ac448f9fbb67f2f8f304a0