ndisc: Do not try to update "updated" time if neighbour has already gone.

Commit 2152caea ("ipv6: Do not depend on rt->n in rt6_probe().")
introduce a bug to try to update "updated" time in neighbour
structure.
Update the "updated" time only if neighbour is available.

Bug was found by Dan Carpenter <dan.carpenter@oracle.com>

Signed-off-by: YOSHIFUJI Hideaki <yoshfuji@linux-ipv6.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv6/route.c b/net/ipv6/route.c
index 2d94d5a..f3328bc 100644
--- a/net/ipv6/route.c
+++ b/net/ipv6/route.c
@@ -492,10 +492,10 @@
 		struct in6_addr mcaddr;
 		struct in6_addr *target;
 
-		neigh->updated = jiffies;
-
-		if (neigh)
+		if (neigh) {
+			neigh->updated = jiffies;
 			write_unlock(&neigh->lock);
+		}
 
 		target = (struct in6_addr *)&rt->rt6i_gateway;
 		addrconf_addr_solict_mult(target, &mcaddr);