net: sched: fix unbalance in the error path of tca_action_flush()

When tca_action_flush() calls the action walk() and gets an error,
a successful call to nla_nest_start() is not followed by a call to
nla_nest_cancel(). It's harmless, as the skb is freed in the error
path - but it's worth to fix this unbalance.
Signed-off-by: Davide Caratti <dcaratti@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/sched/act_api.c

@@ -938,8 +938,10 @@ static int tca_action_flush(struct net *net, struct nlattr *nla,
 		goto out_module_put;
 
 	err = ops->walk(net, skb, &dcb, RTM_DELACTION, ops);
-	if (err <= 0)
+	if (err <= 0) {
+		nla_nest_cancel(skb, nest);
 		goto out_module_put;
+	}
 
 	nla_nest_end(skb, nest);