net: sched: sch_api: set an error msg when qdisc_alloc_handle() fails

This patch sets an error message in extack when the number of qdisc
handles exceeds the maximum. Also the error-code ENOSPC is more
appropriate than ENOMEM in this situation.
Signed-off-by: NIvan Vecera <ivecera@redhat.com>
Reported-by: NLi Shuang <shuali@redhat.com>
Reviewed-by: NStefano Brivio <sbrivio@redhat.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/sched/sch_api.c

@@ -1201,9 +1201,11 @@ static struct Qdisc *qdisc_create(struct net_device *dev,
 	} else {
 		if (handle == 0) {
 			handle = qdisc_alloc_handle(dev);
-			err = -ENOMEM;
-			if (handle == 0)
+			if (handle == 0) {
+				NL_SET_ERR_MSG(extack, "Maximum number of qdisc handles was exceeded");
+				err = -ENOSPC;
 				goto err_out3;
+			}
 		}
 		if (!netif_is_multiqueue(dev))
 			sch->flags |= TCQ_F_ONETXQUEUE;