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/ipv4/ip_tunnel.c b/net/ipv4/ip_tunnel.c
index 50228be..3400d73 100644
--- a/net/ipv4/ip_tunnel.c
+++ b/net/ipv4/ip_tunnel.c
@@ -1041,19 +1041,13 @@
 {
 	struct ip_tunnel *tunnel = netdev_priv(dev);
 	struct iphdr *iph = &tunnel->parms.iph;
-	int i, err;
+	int err;
 
 	dev->destructor	= ip_tunnel_dev_free;
-	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 *ipt_stats;
-		ipt_stats = per_cpu_ptr(dev->tstats, i);
-		u64_stats_init(&ipt_stats->syncp);
-	}
-
 	tunnel->dst_cache = alloc_percpu(struct ip_tunnel_dst);
 	if (!tunnel->dst_cache) {
 		free_percpu(dev->tstats);