openssl: Set some sort of session id context.

Without a session id context and if client certificates are used, OpenSSL
fails the handshake if an attempt is made to reuse an old session. Various
clients could not reconnect after a disconnection because of this.

See https://bugzilla.mozilla.org/show_bug.cgi?id=858394#c34 for a bug
report.

(cherry picked from commit fabc3174fe60b5748964a9cac2118a502b0c0a19 and
commit cee842a82926d6e6295736b76be968806649beee)