percpu: add __percpu sparse annotations to net

Add __percpu sparse annotations to net.

These annotations are to make sparse consider percpu variables to be
in a different address space and warn if accessed without going
through percpu accessors.  This patch doesn't affect normal builds.

The macro and type tricks around snmp stats make things a bit
interesting.  DEFINE/DECLARE_SNMP_STAT() macros mark the target field
as __percpu and SNMP_UPD_PO_STATS() macro is updated accordingly.  All
snmp_mib_*() users which used to cast the argument to (void **) are
updated to cast it to (void __percpu **).

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: David S. Miller <davem@davemloft.net>
Cc: Patrick McHardy <kaber@trash.net>
Cc: Arnaldo Carvalho de Melo <acme@ghostprotocols.net>
Cc: Vlad Yasevich <vladislav.yasevich@hp.com>
Cc: netdev@vger.kernel.org
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/net/neighbour.h b/include/net/neighbour.h
index 7834f47..da1d58b 100644
--- a/include/net/neighbour.h
+++ b/include/net/neighbour.h
@@ -164,7 +164,7 @@
 	rwlock_t		lock;
 	unsigned long		last_rand;
 	struct kmem_cache		*kmem_cachep;
-	struct neigh_statistics	*stats;
+	struct neigh_statistics	__percpu *stats;
 	struct neighbour	**hash_buckets;
 	unsigned int		hash_mask;
 	__u32			hash_rnd;