ocfs2: Depend on configfs heartbeat items.

ocfs2 mounts require a heartbeat region.  Use the new configfs_depend_item()
facility to actually depend on them so they can't go away from under us.

First, teach cluster/nodemanager.c to depend an item on the o2cb subsystem.
Then teach o2hb_register_callbacks to take a UUID and depend on the
appropriate region.  Finally, teach all users of o2hb to pass a UUID or
NULL if they don't require a pin.

Signed-off-by: Joel Becker <joel.becker@oracle.com>
Signed-off-by: Mark Fasheh <mark.fasheh@oracle.com>
diff --git a/fs/ocfs2/cluster/tcp.c b/fs/ocfs2/cluster/tcp.c
index 0b229a9..d58c7dd 100644
--- a/fs/ocfs2/cluster/tcp.c
+++ b/fs/ocfs2/cluster/tcp.c
@@ -1638,8 +1638,8 @@
 
 void o2net_unregister_hb_callbacks(void)
 {
-	o2hb_unregister_callback(&o2net_hb_up);
-	o2hb_unregister_callback(&o2net_hb_down);
+	o2hb_unregister_callback(NULL, &o2net_hb_up);
+	o2hb_unregister_callback(NULL, &o2net_hb_down);
 }
 
 int o2net_register_hb_callbacks(void)
@@ -1651,9 +1651,9 @@
 	o2hb_setup_callback(&o2net_hb_up, O2HB_NODE_UP_CB,
 			    o2net_hb_node_up_cb, NULL, O2NET_HB_PRI);
 
-	ret = o2hb_register_callback(&o2net_hb_up);
+	ret = o2hb_register_callback(NULL, &o2net_hb_up);
 	if (ret == 0)
-		ret = o2hb_register_callback(&o2net_hb_down);
+		ret = o2hb_register_callback(NULL, &o2net_hb_down);
 
 	if (ret)
 		o2net_unregister_hb_callbacks();