tcp: remove unnecessary skb_reset_tail_pointer()

__pskb_trim_head() does not need to reset skb tail pointer.

Also change the comments, __pskb_pull_head() does not exist.
Signed-off-by: NEric Dumazet <edumazet@google.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/ipv4/tcp_output.c

@@ -1328,9 +1328,8 @@ int tcp_fragment(struct sock *sk, struct sk_buff *skb, u32 len,
 	return 0;
 }
 
-/* This is similar to __pskb_pull_head() (it will go to core/skbuff.c
- * eventually). The difference is that pulled data not copied, but
- * immediately discarded.
+/* This is similar to __pskb_pull_tail(). The difference is that pulled
+ * data is not copied, but immediately discarded.
  */
 static int __pskb_trim_head(struct sk_buff *skb, int len)
 {
@@ -1365,7 +1364,6 @@ static int __pskb_trim_head(struct sk_buff *skb, int len)
 	}
 	shinfo->nr_frags = k;
 
-	skb_reset_tail_pointer(skb);
 	skb->data_len -= len;
 	skb->len = skb->data_len;
 	return len;