Fixes serious bug in core related to route filtering.

If protocol announces a route, route is accepted by import filter to
routing table, and later it announces replacement of that route that is
rejected by import filter, old route remains in routing table.

nest/rt-table.c

@@ -636,6 +636,7 @@ rte_update(rtable *table, net *net, struct proto *p, struct proto *src, rte *new
 
 drop:
   rte_free(new);
+  rte_recalculate(table, net, p, src, NULL, NULL);
   rte_update_unlock();
 }