net: cls_u32: be more strict about skip-sw flag

Return an error if user requested skip-sw and the underlaying
hardware cannot handle tc offloads (or offloads are disabled).
Signed-off-by: NJakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/sched/cls_u32.c

@@ -457,10 +457,12 @@ static int u32_replace_hw_hnode(struct tcf_proto *tp,
 	struct tc_to_netdev offload;
 	int err;
 
+	if (!tc_should_offload(dev, flags))
+		return tc_skip_sw(flags) ? -EINVAL : 0;
+
 	offload.type = TC_SETUP_CLSU32;
 	offload.cls_u32 = &u32_offload;
 
-	if (tc_should_offload(dev, flags)) {
 	offload.cls_u32->command = TC_CLSU32_NEW_HNODE;
 	offload.cls_u32->hnode.divisor = h->divisor;
 	offload.cls_u32->hnode.handle = h->handle;
@@ -470,7 +472,6 @@ static int u32_replace_hw_hnode(struct tcf_proto *tp,
 					    tp->protocol, &offload);
 	if (tc_skip_sw(flags))
 		return err;
-	}
 
 	return 0;
 }