Btrfs: Add back the online defragging code

Signed-off-by: Chris Mason <chris.mason@oracle.com>
diff --git a/fs/btrfs/extent_map.h b/fs/btrfs/extent_map.h
index d74a2b3..8409b5c 100644
--- a/fs/btrfs/extent_map.h
+++ b/fs/btrfs/extent_map.h
@@ -14,6 +14,8 @@
 #define EXTENT_LOCKED (1 << 3)
 #define EXTENT_NEW (1 << 4)
 #define EXTENT_DELALLOC (1 << 5)
+#define EXTENT_DEFRAG (1 << 6)
+#define EXTENT_DEFRAG_DONE (1 << 7)
 #define EXTENT_IOBITS (EXTENT_LOCKED | EXTENT_WRITEBACK)