mbedtls_ssl_handshake_params::min_tls_version field

Minimum TLS version to be negotiated. It is set up in the ClientHello writing preparation stage and used throughout the ClientHello writing. Not relevant anymore as soon as the protocol version has been negotiated thus as soon as the ServerHello is received. For a fresh handshake not linked to any previous handshake, it is equal to the configured minimum minor version to be negotiated. When renegotiating or resuming a session, it is equal to the previously negotiated minor version. There is no maximum TLS version field in this handshake context. From the start of the handshake, we need to define a current protocol version for the record layer which we define as the maximum TLS version to be negotiated. The `tls_version` field of the SSL context is used to store this maximum value until it contains the actual negotiated value.