net: fix validate_link_af in rtnetlink core

I'm testing an API that uses IFLA_AF_SPEC attribute.
In the rtnetlink core , the set_link_af() member
of the rtnl_af_ops struct receives the nested attribute
(as I expected), but the validate_link_af() member
receives the parent attribute.
IMO, this patch fixes this.
Signed-off-by: NKurt Van Dijck <kurt.van.dijck@eia.be>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/core/rtnetlink.c

@@ -1121,8 +1121,7 @@ static int validate_linkmsg(struct net_device *dev, struct nlattr *tb[])
 				return -EOPNOTSUPP;
 
 			if (af_ops->validate_link_af) {
-				err = af_ops->validate_link_af(dev,
-							tb[IFLA_AF_SPEC]);
+				err = af_ops->validate_link_af(dev, af);
 				if (err < 0)
 					return err;
 			}