[IPV6]: anycast refcnt fix

This patch fixes a bug in Linux IPv6 stack which caused anycast address
to be added to a device prior DAD has been completed. This led to
incorrect reference count which resulted in infinite wait for
unregister_netdevice completion on interface removal.
Signed-off-by: NMichal Wrobel <xmxwx@asn.pl>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/ipv6/addrconf.c

@@ -400,6 +400,8 @@ static void dev_forward_change(struct inet6_dev *idev)
 			ipv6_dev_mc_dec(dev, &addr);
 	}
 	for (ifa=idev->addr_list; ifa; ifa=ifa->if_next) {
+		if (ifa->flags&IFA_F_TENTATIVE)
+			continue;
 		if (idev->cnf.forwarding)
 			addrconf_join_anycast(ifa);
 		else