Fix build with LibreSSL 2.5.1 and higher.

Fix build with LibreSSL 2.5.1 and higher.

We don't actually care if we use the read or write state; we're only
calculating the cipher/protocol overheads which are the same in both
directions.

In LibreSSL they were all removed in
https://github.com/libressl-portable/openbsd/commit/122ecd906da7
and the read side was restored in
https://github.com/libressl-portable/openbsd/commit/0d7a7d5f5a44
so just use that.

Signed-off-by: Piotr Kubaj <pkubaj@anongoth.pl>
Signed-off-by: David Woodhouse <dwmw2@infradead.org>