Also, update bundled http2 to x/net git rev 0d8126f to include
https://golang.org/cl/30150, the HTTP/2 version of this fix.

Fixes #16002

Change-Id: I8da1ca98250357aec012e3e85c8b13acfa2f3fec
Reviewed-on: https://go-review.googlesource.com/30151
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>