cifs: convert tlink_tree to a rbtree

Radix trees are ideal when you want to track a bunch of pointers and
can't embed a tracking structure within the target of those pointers.
The tradeoff is an increase in memory, particularly if the tree is
sparse.

In CIFS, we use the tlink_tree to track tcon_link structs. A tcon_link
can never be in more than one tlink_tree, so there's no impediment to
using a rb_tree here instead of a radix tree.

Convert the new multiuser mount code to use a rb_tree instead. This
should reduce the memory required to manage the tlink_tree.

Signed-off-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Steve French <sfrench@us.ibm.com>
diff --git a/fs/cifs/cifsglob.h b/fs/cifs/cifsglob.h
index f259e4d..b577bf0 100644
--- a/fs/cifs/cifsglob.h
+++ b/fs/cifs/cifsglob.h
@@ -336,7 +336,8 @@
  * "get" on the container.
  */
 struct tcon_link {
-	unsigned long		tl_index;
+	struct rb_node		tl_rbnode;
+	uid_t			tl_uid;
 	unsigned long		tl_flags;
 #define TCON_LINK_MASTER	0
 #define TCON_LINK_PENDING	1