skbuff: remove some unnecessary operation in skb_segment_list()

gro list uses skb_shinfo(skb)->frag_list to link two skb together,
and NAPI_GRO_CB(p)->last->next is used when there are more skb,
see skb_gro_receive_list(). gso expects that each segmented skb is
linked together using skb->next, so only the first skb->next need
to set to skb_shinfo(skb)-> frag_list when doing gso list segment.

It is the same reason that nskb->next does not need to be set to
list_skb before goto the error handling, because nskb->next already
pointers to list_skb.

And nskb is also the last skb at the end of loop, so remove tail
variable and use nskb instead.
Signed-off-by: Yunsheng Lin <linyunsheng@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/core/skbuff.c

@@ -3732,13 +3732,13 @@ struct sk_buff *skb_segment_list(struct sk_buff *skb,
 	unsigned int tnl_hlen = skb_tnl_header_len(skb);
 	unsigned int delta_truesize = 0;
 	unsigned int delta_len = 0;
-	struct sk_buff *tail = NULL;
 	struct sk_buff *nskb, *tmp;
 	int err;
 
 	skb_push(skb, -skb_network_offset(skb) + offset);
 
 	skb_shinfo(skb)->frag_list = NULL;
+	skb->next = list_skb;
 
 	do {
 		nskb = list_skb;
@@ -3756,17 +3756,8 @@ struct sk_buff *skb_segment_list(struct sk_buff *skb,
 			}
 		}
 
-		if (!tail)
-			skb->next = nskb;
-		else
-			tail->next = nskb;
-
-		if (unlikely(err)) {
-			nskb->next = list_skb;
+		if (unlikely(err))
 			goto err_linearize;
-		}
-
-		tail = nskb;
 
 		delta_len += nskb->len;
 		delta_truesize += nskb->truesize;
@@ -3793,7 +3784,7 @@ struct sk_buff *skb_segment_list(struct sk_buff *skb,
 
 	skb_gso_reset(skb);
 
-	skb->prev = tail;
+	skb->prev = nskb;
 
 	if (skb_needs_linearize(skb, features) &&
 	    __skb_linearize(skb))