Updates http2 to x/net/http2 git rev 292b43b for:

    http2: reject incoming HEADERS in Server on half-closed streams
    https://golang.org/cl/111677

Updates #25023

Change-Id: I479ae9b5b899fb0202e6301d02535fb6aeb4997a
Reviewed-on: https://go-review.googlesource.com/122877Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>