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/net/ipv6/ip6_tunnel.c b/net/ipv6/ip6_tunnel.c
index 5db8d31..8ad59f4 100644
--- a/net/ipv6/ip6_tunnel.c
+++ b/net/ipv6/ip6_tunnel.c
@@ -1502,19 +1502,12 @@
 ip6_tnl_dev_init_gen(struct net_device *dev)
 {
 	struct ip6_tnl *t = netdev_priv(dev);
-	int i;
 
 	t->dev = dev;
 	t->net = dev_net(dev);
-	dev->tstats = alloc_percpu(struct pcpu_sw_netstats);
+	dev->tstats = netdev_alloc_pcpu_stats(struct pcpu_sw_netstats);
 	if (!dev->tstats)
 		return -ENOMEM;
-
-	for_each_possible_cpu(i) {
-		struct pcpu_sw_netstats *ip6_tnl_stats;
-		ip6_tnl_stats = per_cpu_ptr(dev->tstats, i);
-		u64_stats_init(&ip6_tnl_stats->syncp);
-	}
 	return 0;
 }