update LibreSSL support

[semarie]

build tested on OpenBSD 7.2-current (with LibreSSL 3.7.1)

one possible problem is SSL_client_version(). I used SSL_version() as alternative:

• SSL struct is now opaque
• SSL_client_version() is unavailable

but SSL_client_version() doesn't seems very useful, as according to the OpenSSL documentation, it is a partial result:

SSL_client_version() returns the numeric protocol version advertised by the client in the legacy_version field of the ClientHello when initiating the connection. Note that, for TLS, this value will never indicate a version greater than TLSv1.2 even if TLSv1.3 is subsequently negotiated.

It should fixe #209