BUILD: make tune.ssl.keylog available again

BUILD: make tune.ssl.keylog available again

Since commit 04a5a44 ("BUILD: ssl: use HAVE_OPENSSL_KEYLOG instead of
OpenSSL versions") the "tune.ssl.keylog" feature is broken because
HAVE_OPENSSL_KEYLOG does not exist.

Replace this by a HAVE_SSL_KEYLOG which is defined in openssl-compat.h.
Also add an error when not built with the right openssl version.

Must be backported as far as 2.3.