net: don't check skb_count twice

NAPI cache skb_count is being checked twice without condition. Change to
checking the second time only if the first check is run.
Signed-off-by: NSieng Piaw Liew <liew.s.piaw@gmail.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/core/skbuff.c

@@ -175,13 +175,14 @@ static struct sk_buff *napi_skb_cache_get(void)
 	struct napi_alloc_cache *nc = this_cpu_ptr(&napi_alloc_cache);
 	struct sk_buff *skb;
 
-	if (unlikely(!nc->skb_count))
+	if (unlikely(!nc->skb_count)) {
 		nc->skb_count = kmem_cache_alloc_bulk(skbuff_head_cache,
 						      GFP_ATOMIC,
 						      NAPI_SKB_CACHE_BULK,
 						      nc->skb_cache);
-	if (unlikely(!nc->skb_count))
-		return NULL;
+		if (unlikely(!nc->skb_count))
+			return NULL;
+	}
 
 	skb = nc->skb_cache[--nc->skb_count];
 	kasan_unpoison_object_data(skbuff_head_cache, skb);