Force IPv6 garbage collection on device down

We had some problems with devices occasionally hanging with non zero reference count on device destroy until the next time the IPv6 garbage collection timer ran (upto 10s).

To avoid that this patch forces an IPv6 FIB garbage collection on device down.

-Andi

diff -u linux-2.6.5/net/ipv6/ndisc.c-N linux-2.6.5/net/ipv6/ndisc.c
@@ -1403,6 +1403,9 @@
 		neigh_changeaddr(&nd_tbl, dev);
 		fib6_run_gc(0);
 		break;
+	case NETDEV_UNREGISTER:
+		fib6_run_gc(0);
+		break;
 	default:
 		break;
 	}