net: skb_queue_purge_reason() optimizations

1) Exit early if the list is empty.

2) splice the list into a local list,
   so that we block hard irqs only once.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://lore.kernel.org/r/20231003181920.3280453-1-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Author: edumazet

net/core/skbuff.c

@@ -3722,10 +3722,19 @@ EXPORT_SYMBOL(skb_dequeue_tail);
 void skb_queue_purge_reason(struct sk_buff_head *list,
 			    enum skb_drop_reason reason)
 {
-	struct sk_buff *skb;
+	struct sk_buff_head tmp;
+	unsigned long flags;
+
+	if (skb_queue_empty_lockless(list))
+		return;
+
+	__skb_queue_head_init(&tmp);
+
+	spin_lock_irqsave(&list->lock, flags);
+	skb_queue_splice_init(list, &tmp);
+	spin_unlock_irqrestore(&list->lock, flags);
 
-	while ((skb = skb_dequeue(list)) != NULL)
-		kfree_skb_reason(skb, reason);
+	__skb_queue_purge_reason(&tmp, reason);
 }
 EXPORT_SYMBOL(skb_queue_purge_reason);