Add SSL_CTX_get_max_proto_version() not in openssl 1.0

Add SSL_CTX_get_max_proto_version() not in openssl 1.0

- No change in functionality. This is used in a subsequent
  patch for extending TLS1.2 support with cryptoapicert

Signed-off-by: Selva Nair <selva.nair@gmail.com>
Acked-by: Gert Doering <gert@greenie.muc.de>
Message-Id: <1516468294-32635-1-git-send-email-selva.nair@gmail.com>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg16304.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>
(cherry-picked with 2.4/0.9.8 amendments from commit
 9e272106029a41b2110c10334ba8cae0f4afb1b4)