configure.ac: check for SSL_OP_NO_TICKET flag in OpenSSL

configure.ac: check for SSL_OP_NO_TICKET flag in OpenSSL

SSL_OP_NO_TICKET tells OpenSSL to disable "stateless session resumption".
This is something we do not want nor need, but could potentially be used
for a future attack. OpenVPN 2.4 requires the flag to be set and will fail
configure if the flag is not present.
Acked-by: Gert Doering <gert@greenie.muc.de>
Message-Id: <CAA1AbxJh17KYmVU1BVa5kp4iJsUJT+xnXp0rVU_3g3c5hPnqDQ@mail.gmail.com>
URL: http://article.gmane.org/gmane.network.openvpn.devel/8389

Signed-off-by: Gert Doering <gert@greenie.muc.de>