ssh: add hmac-sha2-256.

Fixes golang/go#10274

Change-Id: Id8386828ee92ccc6cba5197831cdb8b2ce0cd648
Reviewed-on: https://go-review.googlesource.com/8353
Reviewed-by: Adam Langley <agl@golang.org>
Run-TryBot: Adam Langley <agl@golang.org>
2 files changed