Encrypt-then-MAC support

[Yury Korolev <yurykorolev@xxxxxx>]

Hi,

Any plans to support etm?

currently getting

`
kex error : no match for method mac algo client->server: server [[hmac-sha2-512-etm@xxxxxxxxxxx](mailto:hmac-sha2-512-etm@xxxxxxxxxxx),[hmac-sha2-256-etm@xxxxxxxxxxx](mailto:hmac-sha2-256-etm@xxxxxxxxxxx),[umac-128-etm@xxxxxxxxxxx](mailto:umac-128-etm@xxxxxxxxxxx)], client [hmac-sha2-256,hmac-sha2-512,hmac-sha1]
`

Thank you.