Specify session context for OpenSSL clients

Specify session context for OpenSSL clients

Reconnecting to ngIRCd 22.1 built with OpenSSL with some OpenSSL
clients, including Pidgin and stunnel 5.06, attempts to reuse a session
and fails due to the absence of this line.

The error message in syslog from ngIRCd is:

> SSL protocol error: SSL_accept (error:140D9115:SSL
> routines:SSL_GET_PREV_SESSION:session id context uninitialized)

This patch appears to fix the problem for both Pidgin and stunnel; it
may work for other OpenSSL clients that attempt to re-use sessions.

*   <https://github.com/ngircd/ngircd/issues/182>
*   <https://developer.pidgin.im/ticket/11568>
*   <https://www.openssl.org/docs/ssl/SSL_CTX_set_session_id_context.html>