vendor: update golang.org/x/net/http2/hpack

Updates bundled golang.org/x/net/http2/hpack to x/net git rev 22bb95c5e for:

   http2/hpack: lazily build huffman table on first use
   https://golang.org/cl/127275

   http2/hpack: reduce memory for huffman decoding table
   https://golang.org/cl/127235

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

And a typo & gofmt CL.

Updates #25023

Change-Id: I7027fdb4982305aa671d811fe87f61e5df0f8e0e
Reviewed-on: https://go-review.googlesource.com/127355


Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Andrew Bonventre <andybons@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>