net: add prefetch() in skb_defer_free_flush()

skb_defer_free_flush() is becoming more important these days.

Add a prefetch operation to reduce latency a bit on some
platforms like AMD EPYC 7B12.

On more recent cpus, a stall happens when reading skb_shinfo().
Avoiding it will require a more elaborate strategy.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Acked-by: Paolo Abeni <pabeni@redhat.com>
Link: https://patch.msgid.link/20251106085500.2438951-1-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

net/core/dev.c

@@ -6782,6 +6782,7 @@ static void skb_defer_free_flush(void)
 		free_list = llist_del_all(&sdn->defer_list);
 
 		llist_for_each_entry_safe(skb, next, free_list, ll_node) {
+			prefetch(next);
 			napi_consume_skb(skb, 1);
 		}
 	}