[IPV6]: Set dead flag on idev if snmp6_register_dev() fails.

net/ipv6/addrconf.c

@@ -343,6 +343,7 @@ static struct inet6_dev * ipv6_add_dev(struct net_device *dev)
 				"%s(): cannot create /proc/net/dev_snmp6/%s\n",
 				__FUNCTION__, dev->name));
 			neigh_parms_release(&nd_tbl, ndev->nd_parms);
+			ndev->dead = 1;
 			in6_dev_finish_destroy(ndev);
 			return NULL;
 		}