net: sched: Clarify error message when qdisc kind is unknown

stable inclusion
from stable-v5.10.101
commit 3d0eafd459b2cd32c3044043addc4902c5911ffa
bugzilla: https://gitee.com/openeuler/kernel/issues/I5669Z

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=3d0eafd459b2cd32c3044043addc4902c5911ffa

--------------------------------

[ Upstream commit 973bf8fd ]

When adding a tc rule with a qdisc kind that is not supported or not
compiled into the kernel, the kernel emits the following error: "Error:
Specified qdisc not found.". Found via tdc testing when ETS qdisc was not
compiled in and it was not obvious right away what the message meant
without looking at the kernel code.

Change the error message to be more explicit and say the qdisc kind is
unknown.
Signed-off-by: NVictor Nogueira <victor@mojatatu.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>
Signed-off-by: NSasha Levin <sashal@kernel.org>
Signed-off-by: NYu Liao <liaoyu15@huawei.com>
Reviewed-by: NWei Li <liwei391@huawei.com>
Signed-off-by: NZheng Zengkai <zhengzengkai@huawei.com>

net/sched/sch_api.c

@@ -1204,7 +1204,7 @@ static struct Qdisc *qdisc_create(struct net_device *dev,
 
 	err = -ENOENT;
 	if (!ops) {
-		NL_SET_ERR_MSG(extack, "Specified qdisc not found");
+		NL_SET_ERR_MSG(extack, "Specified qdisc kind is unknown");
 		goto err_out;
 	}