Updates to x/net rev 195180cf
(golang.org/cl/17134, http2: merge duplicate Transport dials)

Change-Id: I50b9c73b30c6a21e725aad80126b713d8b0fa362
Reviewed-on: https://go-review.googlesource.com/17261Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>