tls: Support a maximum TLS version to negotiate using TLS socket abstraction

src/libpttls/pt_tls_client.c

@@ -85,7 +85,7 @@ static bool make_connection(private_pt_tls_client_t *this)
 	}
 
 	this->tls = tls_socket_create(FALSE, this->server, this->client, fd,
-								  NULL, FALSE);
+								  NULL, TLS_1_2, FALSE);
 	if (!this->tls)
 	{
 		close(fd);

src/libpttls/pt_tls_server.c

@@ -532,7 +532,7 @@ pt_tls_server_t *pt_tls_server_create(identification_t *server, int fd,
 			.destroy = _destroy,
 		},
 		.state = PT_TLS_SERVER_VERSION,
-		.tls = tls_socket_create(TRUE, server, NULL, fd, NULL, FALSE),
+		.tls = tls_socket_create(TRUE, server, NULL, fd, NULL, TLS_1_2, FALSE),
 		.tnccs = (tls_t*)tnccs,
 		.auth = auth,
 	);