Revert new ordering for route retractions.

That's not the issue -- the issue is with the kernel dropping routes when
we loose an IP address.

rolling back:

Fri Mar  4 21:26:15 CET 2011  Juliusz Chroboczek <jch@pps.jussieu.fr>
  * Fix ordering of netlink messages when making a route unreachable.

  This should fix:

    netlink_read: File exists
    netlink_read: No such process

    M ./kernel_netlink.c -1 +1

kernel_netlink.c

@@ -796,7 +796,7 @@ kernel_route(int operation, const unsigned char *dest, unsigned short plen,
         /* It is better to add the new route before removing the old
            one, to avoid losing packets.  However, this only appears
            to work if the metrics are different. */
-        if(newmetric != metric && newmetric < KERNEL_INFINITY) {
+        if(newmetric != metric) {
             rc = kernel_route(ROUTE_ADD, dest, plen,
                               newgate, newifindex, newmetric,
                               NULL, 0, 0);