niu: don't count tx error twice in case of headroom realloc fails

Fixes: a3138df9 ("[NIU]: Add Sun Neptune ethernet driver.")
Signed-off-by: NJiri Pirko <jiri@resnulli.us>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/ethernet/sun/niu.c

@@ -6658,10 +6658,8 @@ static netdev_tx_t niu_start_xmit(struct sk_buff *skb,
 		struct sk_buff *skb_new;
 
 		skb_new = skb_realloc_headroom(skb, len);
-		if (!skb_new) {
-			rp->tx_errors++;
+		if (!skb_new)
 			goto out_drop;
-		}
 		kfree_skb(skb);
 		skb = skb_new;
 	} else