net: sched: refine extack messages in tcf_change_indev

Add an error message when device wasn't found.
While there, also set the bad attribute's offset in extack.

Signed-off-by: Guillaume Nault <gnault@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/pkt_cls.h

@@ -502,12 +502,16 @@ tcf_change_indev(struct net *net, struct nlattr *indev_tlv,
 	struct net_device *dev;
 
 	if (nla_strlcpy(indev, indev_tlv, IFNAMSIZ) >= IFNAMSIZ) {
-		NL_SET_ERR_MSG(extack, "Interface name too long");
+		NL_SET_ERR_MSG_ATTR(extack, indev_tlv,
+				    "Interface name too long");
 		return -EINVAL;
 	}
 	dev = __dev_get_by_name(net, indev);
-	if (!dev)
+	if (!dev) {
+		NL_SET_ERR_MSG_ATTR(extack, indev_tlv,
+				    "Network device not found");
 		return -ENODEV;
+	}
 	return dev->ifindex;
 }