To decreae latency this add support for TFO and TLS Session Tickets. As OpenSSL wouldn't let you easily set a different function all written data is temporarily cached and therefore needs to be flushed after each SSL function which can write data.
This provides basic OpenSSL support without optimizations like TCP Fast Open and TLS Session Tickets.
Notice only a single SSL library can be enabled at a time and therefore journald functions provided by GnuTLS will be disabled when using OpenSSL.
Fixes#9531
During handshake and TLS session closing, messages needs to be exchanged. Therefore this patch overrides the requested IO events for the TCP stream when the TLS is waiting for sending or receiving of messages during theses periods. This fixes issues with correctly closing the TLS stream and prevents the handshake from hanging in rare cases (not seen yet).
