Add stub for route_interferes.

route.c

@@ -290,6 +290,12 @@ route_expired(struct route *route)
     return route->time < now.tv_sec - route->hold_time;
 }
 
+int
+route_interferes(struct route *route, struct network *net)
+{
+    return 1;
+}
+
 int
 update_feasible(struct source *src,
                 unsigned short seqno, unsigned short refmetric)

route.h

@@ -58,6 +58,7 @@ void switch_route(struct route *old, struct route *new);
 int route_feasible(struct route *route);
 int route_old(struct route *route);
 int route_expired(struct route *route);
+int route_interferes(struct route *route, struct network *net);
 int update_feasible(struct source *src,
                     unsigned short seqno, unsigned short refmetric);
 struct route *find_best_route(const unsigned char *prefix, unsigned char plen,