[NET_SCHED]: act_api: fix skb leak in error path

The skb is allocated by the function, so it needs to be freed instead
of trimmed on overrun.

Coverity #614
Signed-off-by: NPatrick McHardy <kaber@trash.net>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/sched/act_api.c

@@ -707,7 +707,7 @@ static int tcf_add_notify(struct tc_action *a, u32 pid, u32 seq, int event,
 
 rtattr_failure:
 nlmsg_failure:
-	skb_trim(skb, b - skb->data);
+	kfree_skb(skb);
 	return -1;
 }