net: remove unnecessary NULL checking in napi_consume_skb()

When budget is non-zero, skb_unref() has already handled the
NULL checking.

When budget is zero, the dev_consume_skb_any() has handled NULL
checking in __dev_kfree_skb_irq(), or dev_kfree_skb() which also
ultimately call skb_unref().

So remove the unnecessary checking in napi_consume_skb().
Signed-off-by: NYunsheng Lin <linyunsheng@huawei.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/core/skbuff.c

@@ -895,9 +895,6 @@ void __kfree_skb_defer(struct sk_buff *skb)
 
 void napi_consume_skb(struct sk_buff *skb, int budget)
 {
-	if (unlikely(!skb))
-		return;
-
 	/* Zero budget indicate non-NAPI context called us, like netpoll */
 	if (unlikely(!budget)) {
 		dev_consume_skb_any(skb);