Lockdep: add lockdep_set_class_and_subclass() and lockdep_set_subclass()

This annotation makes it possible to assign a subclass on lock init. This
annotation is meant to reduce the _nested() annotations by assigning a
default subclass.

One could do without this annotation and rely on lockdep_set_class()
exclusively, but that would require a manual stack of struct lock_class_key
objects.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>
diff --git a/net/core/sock.c b/net/core/sock.c
index b77e155..d472db4 100644
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -823,7 +823,7 @@
 				   af_family_slock_key_strings[sk->sk_family]);
 	lockdep_init_map(&sk->sk_lock.dep_map,
 			 af_family_key_strings[sk->sk_family],
-			 af_family_keys + sk->sk_family);
+			 af_family_keys + sk->sk_family, 0);
 }
 
 /**