Renamed in GnuTLS 3.8.1.

Index: gnutls-dtls.c
--- gnutls-dtls.c.orig
+++ gnutls-dtls.c
@@ -410,7 +410,7 @@ int start_dtls_handshake(struct openconnect_info *vpni
 	gnutls_session_t dtls_ssl;
 	int err, ret;
 
-	err = gnutls_init(&dtls_ssl, GNUTLS_CLIENT|GNUTLS_DATAGRAM|GNUTLS_NONBLOCK|GNUTLS_NO_EXTENSIONS);
+	err = gnutls_init(&dtls_ssl, GNUTLS_CLIENT|GNUTLS_DATAGRAM|GNUTLS_NONBLOCK|GNUTLS_NO_DEFAULT_EXTENSIONS);
 	if (err) {
 		vpn_progress(vpninfo, PRG_ERR,
 			     _("Failed to initialize DTLS: %s\n"),