net: introduce netdev_alloc_pcpu_stats() for drivers

There are many drivers calling alloc_percpu() to allocate pcpu stats
and then initializing ->syncp. So just introduce a helper function for them.

Cc: David S. Miller <davem@davemloft.net>
Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/drivers/net/dummy.c b/drivers/net/dummy.c
index bd8f84b..1656317 100644
--- a/drivers/net/dummy.c
+++ b/drivers/net/dummy.c
@@ -88,16 +88,10 @@
 
 static int dummy_dev_init(struct net_device *dev)
 {
-	int i;
-	dev->dstats = alloc_percpu(struct pcpu_dstats);
+	dev->dstats = netdev_alloc_pcpu_stats(struct pcpu_dstats);
 	if (!dev->dstats)
 		return -ENOMEM;
 
-	for_each_possible_cpu(i) {
-		struct pcpu_dstats *dstats;
-		dstats = per_cpu_ptr(dev->dstats, i);
-		u64_stats_init(&dstats->syncp);
-	}
 	return 0;
 }