Add the diffie-hellman-group-exchange-sha256 defined in RFC 4419 to the list of supported key exchange algorithms for ssh. The server half is only a minimal implementation to satisfy the automated tests. Fixes golang/go#17230 Change-Id: I25880a564347fd9b4738dd2ed1e347cd5d2e21bb GitHub-Last-Rev: 9f0b8d02c0c96e9baf00cdf1cf063ff834245443 GitHub-Pull-Request: golang/crypto#87 Reviewed-on: https://go-review.googlesource.com/c/crypto/+/174257 Run-TryBot: Han-Wen Nienhuys <hanwen@google.com> TryBot-Result: Gobot Gobot <gobot@golang.org> Reviewed-by: Han-Wen Nienhuys <hanwen@google.com>