Add support for tls-ciphersuites for TLS 1.3

Add support for tls-ciphersuites for TLS 1.3

OpenSSL 1.1.1 introduces a separate list for TLS 1.3 ciphers. As these
interfaces are meant to be user facing or not exposed at all and we
expose the tls-cipher interface, we should also expose tls-cipherlist.

Combining both settings into tls-cipher would add a lot of glue logic
that needs to be maintained and is error prone. On top of that, users
should not set either settings unless absolutely required.

OpenSSL's own s_client/s_server also expose both settings and I believe
most other software will too:

 -cipher val         Specify TLSv1.2 and below cipher list to be used
 -ciphersuites val   Specify TLSv1.3 ciphersuites to be used

For mbed TLS only the future can tell if we will see a combined or also
two separate lists.
Acked-by: Steffan Karger <steffan.karger@fox-it.com>
Message-Id: <20181007215539.32761-1-arne@rfc2549.org>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg17626.html

Signed-off-by: Gert Doering <gert@greenie.muc.de>
(cherry picked from commit ea4ee31333a0cddb5c8dd4185f9426df13c76947)