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/openvswitch/datapath.c b/net/openvswitch/datapath.c
index e9a48ba..3a95406 100644
--- a/net/openvswitch/datapath.c
+++ b/net/openvswitch/datapath.c
@@ -1215,18 +1215,12 @@
 	if (err)
 		goto err_free_dp;
 
-	dp->stats_percpu = alloc_percpu(struct dp_stats_percpu);
+	dp->stats_percpu = netdev_alloc_pcpu_stats(struct dp_stats_percpu);
 	if (!dp->stats_percpu) {
 		err = -ENOMEM;
 		goto err_destroy_table;
 	}
 
-	for_each_possible_cpu(i) {
-		struct dp_stats_percpu *dpath_stats;
-		dpath_stats = per_cpu_ptr(dp->stats_percpu, i);
-		u64_stats_init(&dpath_stats->sync);
-	}
-
 	dp->ports = kmalloc(DP_VPORT_HASH_BUCKETS * sizeof(struct hlist_head),
 			    GFP_KERNEL);
 	if (!dp->ports) {