mm: memcontrol: generalize the socket accounting jump label

The unified hierarchy memory controller is going to use this jump label
as well to control the networking callbacks.  Move it to the memory
controller code and give it a more generic name.

Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Michal Hocko <mhocko@suse.com>
Reviewed-by: Vladimir Davydov <vdavydov@virtuozzo.com>
Acked-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index eaaa861..08ef3d2 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -291,6 +291,9 @@
 /* Writing them here to avoid exposing memcg's inner layout */
 #if defined(CONFIG_INET) && defined(CONFIG_MEMCG_KMEM)
 
+struct static_key memcg_sockets_enabled_key;
+EXPORT_SYMBOL(memcg_sockets_enabled_key);
+
 void sock_update_memcg(struct sock *sk)
 {
 	struct mem_cgroup *memcg;