Updates http2 to x/net/http2 git rev 97aa3a539 for:

    http2: dynamic table updates must occur first
    https://golang.org/cl/111681

    http2: receiving too much data is a protocol error
    https://golang.org/cl/111679

    http2: correct overflow protection
    https://golang.org/cl/111675

    http2: make Server send GOAWAY if Handler sets "Connection: close" header
    https://golang.org/cl/121415

Fixes #20977

Change-Id: I9b8659b5191409ed007e2d911913763bcbabb7cc
Reviewed-on: https://go-review.googlesource.com/121695Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>