Automated rollback of internal change 130388085.

Automated rollback of internal change 130388085.

relnote: Rollback flag quic_enforce_mtu_limit. Never enabled.

*** Original change description ***

Original relnote: Use a small QUIC MTU when a potentially fragmented
packet is received. Guarded by quic_enforce_mtu_limit.

If QuicRxRing is enabled, the UDP listener will only receive "strange"
packets
(fragmented, IPv6 extension headers, etc.). If a connection is created
from a
packet on the UDP listener, shrink the connection's MTU to 1214 for its
lifetime.

***
Merge internal change: 135261089

BUG=

[Zhongyi Shi, 2016-10-10 23:36:14]

zhongyi@chromium.org changed reviewers:
+ rch@chromium.org

[Ryan Hamilton, 2016-10-11 02:34:16]

lgtm

[Zhongyi Shi, 2016-10-11 03:52:07]

The CQ bit was checked by zhongyi@chromium.org to run a CQ dry run

[commit-bot: I haz the power, 2016-10-11 03:52:14]

Dry run: CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[commit-bot: I haz the power, 2016-10-11 04:24:25]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2016-10-11 04:24:28]

Dry run: Try jobs failed on following builders:
  cast_shell_linux on master.tryserver.chromium.linux (JOB_FAILED,
http://build.chromium.org/p/tryserver.chromium.linux/builders/cast_shell_linu...)