CHROMIUM: Revert SFE IPv6 asymmetric QoS

Revert SFE asymmetric QoS support for IPv6 introduced in CL
chromium:1717644. In addition to the asymmetric QoS support this also
reverts the handling of ICMP error messages that trigger recreation
of flow state for an embedded IP packet.

This is a workaround to prevent IPv6 forwarding from wedging when
there is simultaneous high rate IPv4 traffic.

BUG=b:139326716, b:140608418
TEST=Ran lab tests with IPv6-only client successfully accessing
     Internet while Stadia emulator simultaneously streaming IPv4.

Change-Id: If14bb0d2e07923a41cac09339844dbaa82b62fbc
Signed-off-by: Danny J. Mitzel <mitzel@google.com>
Reviewed-on: https://chromium-review.googlesource.com/1799664


Tested-by: Danny Mitzel <mitzel@google.com>
Commit-Ready: Kan Yan <kyan@chromium.org>
Legacy-Commit-Queue: Commit Bot <commit-bot@chromium.org>
Reviewed-by: Kevin Hayes <kevinhayes@google.com>
Reviewed-by: Kan Yan <kyan@chromium.org>