Add route_metric option

To be able to keep different routes from several running l2tpns instances.

l2tpns.h

@@ -785,6 +785,7 @@ typedef struct
 	in_addr_t	peer_address;
 	struct in6_addr ipv6_prefix;			// Our IPv6 network pool.
 	uint16_t	route_protocol;			// Route protocol number to use
+	int		route_metric;			// Route metric
 	int		send_garp;			// Set to true to garp for vip address on startup
 
 	int		dump_speed;