It was causing mysterious fuzzing failure because it affects the
unmarshaling of the secureNegotiationSupported field.

Change-Id: Id396b84eab90a3b22fb6e306b10bdd7e39707012
Reviewed-on: https://go-review.googlesource.com/60912
Run-TryBot: Filippo Valsorda <hi@filippo.io>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Adam Langley <agl@golang.org>