From x/net git rev c7086645de2.

Updates #16704

Change-Id: I4d642478fc69a52c973964845fca2fd402716e57
Reviewed-on: https://go-review.googlesource.com/68091Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>