netdev: set __percpu attribute on netdev_alloc_pcpu_stats

This patch fixes sparse warnings in vlan driver.
It propagates the sparse __percpu attribute from alloc_percpu
into netdev_alloc_pcpu_stats. I expect it may trigger additional
sparse warnings from other drivers that are missing the __percpu
attribute.
Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
Acked-by: Cong Wang <cwang@twopensource.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/netdevice.h

@@ -1812,7 +1812,7 @@ struct pcpu_sw_netstats {
 
 #define netdev_alloc_pcpu_stats(type)				\
 ({								\
-	typeof(type) *pcpu_stats = alloc_percpu(type);		\
+	typeof(type) __percpu *pcpu_stats = alloc_percpu(type); \
 	if (pcpu_stats)	{					\
 		int i;						\
 		for_each_possible_cpu(i) {			\