openvpn: add handling for route-pre-down option

OpenVPN 2.3 added a route-pre-down option, to run a command before
routes are removed upon disconnection.

Signed-off-by: Jeffery To <jeffery.to@gmail.com>

SVN-Revision: 47134

package/network/services/openvpn/files/openvpn.init

@@ -120,7 +120,7 @@ start_instance() {
 		redirect_gateway remap_usr1 remote remote_cert_eku remote_cert_ku remote_cert_tls \
 		reneg_bytes reneg_pkts reneg_sec \
 		replay_persist replay_window resolv_retry route route_delay route_gateway \
-		route_metric route_up rport script_security secret server server_bridge setenv shaper sndbuf \
+		route_metric route_pre_down route_up rport script_security secret server server_bridge setenv shaper sndbuf \
 		socks_proxy status status_version syslog tcp_queue_limit tls_auth \
 		tls_cipher tls_remote tls_timeout tls_verify tmp_dir topology tran_window \
 		tun_mtu tun_mtu_extra txqueuelen user verb down push up \