ipv6: Only act upon NETDEV_*_TYPE_CHANGE if we have ipv6 addresses

An interface changing type may not have IPv6 addresses. Don't
call the address configuration type change in this case.
Signed-off-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv6/addrconf.c

@@ -3287,7 +3287,8 @@ static int addrconf_notify(struct notifier_block *this, unsigned long event,
 
 	case NETDEV_PRE_TYPE_CHANGE:
 	case NETDEV_POST_TYPE_CHANGE:
-		addrconf_type_change(dev, event);
+		if (idev)
+			addrconf_type_change(dev, event);
 		break;
 	}