libssh: security bump to version 0.8.4

libssh: security bump to version 0.8.4

Fixes CVE-2018-10933: authentication bypass vulnerability in the server
code. By presenting the server an SSH2_MSG_USERAUTH_SUCCESS message in
place of the SSH2_MSG_USERAUTH_REQUEST message which the server would
expect to initiate authentication, the attacker could successfully
authenticate without any credentials.

  https://www.libssh.org/security/advisories/CVE-2018-10933.txt

Drop an upstream patch.

Cc: Scott Fan <fancp2007@gmail.com>
Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>