Unconditionally update routes going through a neighbour on IHU.

The logic that attempted to optimise this away was buggy since it
wasn't taking IHU expiration times into account.  At any rate,
this optimisation is probably not worth the complexity.

message.c

@@ -289,11 +289,10 @@ parse_packet(const unsigned char *from, struct interface *ifp,
                    format_address(from), ifp->name,
                    format_address(address));
             if(message[2] == 0 || interface_ll_address(ifp, address)) {
-                int changed = txcost != neigh->txcost;
                 neigh->txcost = txcost;
                 neigh->ihu_time = now;
                 neigh->ihu_interval = interval;
-                update_neighbour_metric(neigh, changed);
+                update_neighbour_metric(neigh, 1);
                 if(interval > 0)
                     schedule_neighbours_check(interval * 10 * 3, 0);
             }