ssl_openssl: Use uint16_t internally for TLS versions

ssl_openssl: Use uint16_t internally for TLS versions

libressl changed the API for the involved functions. Since
uint16_t is a true subset of int it should be safe to switch
to that for all OpenSSL variants.

One trivial drive-by fix in unrelated code to be able
to enable -Wconversion fully for the file. This just
adds a cast where the comment says we intend a cast.

Change-Id: I9ea87531afb553f789289787403900a4758b8e1c
Signed-off-by: Frank Lichtenheld <frank@lichtenheld.com>
Acked-by: MaxF <max@max-fillinger.net>
Gerrit URL: https://gerrit.openvpn.net/c/openvpn/+/1212
Message-Id: <20250924150300.29318-1-gert@greenie.muc.de>
URL: https://sourceforge.net/p/openvpn/mailman/message/59238230/
Signed-off-by: Gert Doering <gert@greenie.muc.de>