btrfs: make OWNER_REF_KEY type value smallest among inline refs

BTRFS_EXTENT_OWNER_REF_KEY is the type of simple quotas extent owner
refs. This special inline ref goes in front of all other inline refs.

In general, inline refs have a required sorted order s.t. type never
decreases (among other requirements). This was recently reified into a
tree-checker and fsck rule, which broke simple quotas. To be fair,
though, in a sense, the new owner ref item had also violated that not
yet fully enforced requirement.

This fix brings the owner ref item into compliance with the requirement
that inline ref type never decrease.

btrfs/301 exercises this behavior and should pass again with this fix.

Fixes: d9a620f7 ("btrfs: new inline ref storing owning subvol of data extents")
Signed-off-by: Boris Burkov <boris@bur.io>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

include/uapi/linux/btrfs_tree.h

@@ -219,6 +219,22 @@
  */
 #define BTRFS_METADATA_ITEM_KEY	169
 
+/*
+ * Special inline ref key which stores the id of the subvolume which originally
+ * created the extent. This subvolume owns the extent permanently from the
+ * perspective of simple quotas. Needed to know which subvolume to free quota
+ * usage from when the extent is deleted.
+ *
+ * Stored as an inline ref rather to avoid wasting space on a separate item on
+ * top of the existing extent item. However, unlike the other inline refs,
+ * there is one one owner ref per extent rather than one per extent.
+ *
+ * Because of this, it goes at the front of the list of inline refs, and thus
+ * must have a lower type value than any other inline ref type (to satisfy the
+ * disk format rule that inline refs have non-decreasing type).
+ */
+#define BTRFS_EXTENT_OWNER_REF_KEY	172
+
 #define BTRFS_TREE_BLOCK_REF_KEY	176
 
 #define BTRFS_EXTENT_DATA_REF_KEY	178
@@ -233,14 +249,6 @@
 
 #define BTRFS_SHARED_DATA_REF_KEY	184
 
-/*
- * Special inline ref key which stores the id of the subvolume which originally
- * created the extent. This subvolume owns the extent permanently from the
- * perspective of simple quotas. Needed to know which subvolume to free quota
- * usage from when the extent is deleted.
- */
-#define BTRFS_EXTENT_OWNER_REF_KEY	188
-
 /*
  * block groups give us hints into the extent allocation trees.  Which
  * blocks are free etc etc