net: sched: report ndo_setup_tc failures via extack

Help end-users of the 'tc' command to see if the drivers ndo_setup_tc
function call fails. Troubleshooting when this happens is non-trivial
(see full process here[1]), and results in net_device getting assigned
the 'qdisc noop', which will drop all TX packets on the interface.

[1]: https://github.com/xdp-project/xdp-project/blob/master/areas/arm64/board_nxp_ls1088/nxp-board04-troubleshoot-qdisc.orgSigned-off-by: NJesper Dangaard Brouer <brouer@redhat.com>
Tested-by: NIoana Ciornei <ioana.ciornei@nxp.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/sched/cls_api.c

@@ -735,8 +735,11 @@ static int tcf_block_offload_cmd(struct tcf_block *block,
 	INIT_LIST_HEAD(&bo.cb_list);
 
 	err = dev->netdev_ops->ndo_setup_tc(dev, TC_SETUP_BLOCK, &bo);
-	if (err < 0)
+	if (err < 0) {
+		if (err != -EOPNOTSUPP)
+			NL_SET_ERR_MSG(extack, "Driver ndo_setup_tc failed");
 		return err;
+	}
 
 	return tcf_block_setup(block, &bo);
 }