When we no longer need a read buffer or a write buffer for a
given SSL, then release the memory we were using to hold it.
Using this flag can save around 34k per idle SSL connection.
This flag has no effect on SSL v2 connections, or on DTLS
If that description is accurate, then this patch just wastes some
CPU cycles. Postfix does not have idle TLS connections, except for
a fraction of a second when a TLS-encrypted connection is saved to
the connection cache. Such conections are saved only when there is
a steady flow of mail to the same destionstion, so they are reused