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_gre.c b/net/ipv6/ip6_gre.c
index f3ffb43..c98338b 100644
--- a/net/ipv6/ip6_gre.c
+++ b/net/ipv6/ip6_gre.c
@@ -1454,7 +1454,6 @@
 static int ip6gre_tap_init(struct net_device *dev)
 {
 	struct ip6_tnl *tunnel;
-	int i;
 
 	tunnel = netdev_priv(dev);
 
@@ -1464,16 +1463,10 @@
 
 	ip6gre_tnl_link_config(tunnel, 1);
 
-	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 *ip6gre_tap_stats;
-		ip6gre_tap_stats = per_cpu_ptr(dev->tstats, i);
-		u64_stats_init(&ip6gre_tap_stats->syncp);
-	}
-
 	return 0;
 }