ssl_dtls_to_tls_version
if ((max_version = ssl_dtls_to_tls_version(proto_ver)) == 0)
peer_tls_version = ssl_dtls_to_tls_version(peer_ver);
server_tls_version = ssl_dtls_to_tls_version(server_version);
if ((min_version = ssl_dtls_to_tls_version(proto_ver)) == 0)