ssh: Add the hmac-sha2-256-etm@openssh.com algorithm

Fixes golang/go#17676

Change-Id: I96c51431b174898a6bc0f6bec7f4561d5d64819f
Reviewed-on: https://go-review.googlesource.com/35513
Reviewed-by: Han-Wen Nienhuys <hanwen@google.com>
Run-TryBot: Han-Wen Nienhuys <hanwen@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
5 files changed