net: make struct napi_alloc_cache::skb_count unsigned int

size_t is way too much for an integer not exceeding 64.

Space savings: 10 bytes!

	add/remove: 0/0 grow/shrink: 0/3 up/down: 0/-10 (-10)
	function                                     old     new   delta
	napi_consume_skb                             165     163      -2
	__kfree_skb_flush                             56      53      -3
	__kfree_skb_defer                             97      92      -5
	Total: Before=154865639, After=154865629, chg -0.00%
Signed-off-by: NAlexey Dobriyan <adobriyan@gmail.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/core/skbuff.c

@@ -354,7 +354,7 @@ EXPORT_SYMBOL(build_skb);
 
 struct napi_alloc_cache {
 	struct page_frag_cache page;
-	size_t skb_count;
+	unsigned int skb_count;
 	void *skb_cache[NAPI_SKB_CACHE_SIZE];
 };