Btrfs: disable snapshot aware defrag for now

It's just broken and it's taking a lot of effort to fix it, so for now just
disable it so people can defrag in peace.  Thanks,

Cc: stable@vger.kernel.org
Signed-off-by: NJosef Bacik <jbacik@fb.com>
Signed-off-by: NChris Mason <clm@fb.com>

fs/btrfs/inode.c

@@ -2629,7 +2629,7 @@ static int btrfs_finish_ordered_io(struct btrfs_ordered_extent *ordered_extent)
 			EXTENT_DEFRAG, 1, cached_state);
 	if (ret) {
 		u64 last_snapshot = btrfs_root_last_snapshot(&root->root_item);
-		if (last_snapshot >= BTRFS_I(inode)->generation)
+		if (0 && last_snapshot >= BTRFS_I(inode)->generation)
 			/* the inode is shared */
 			new = record_old_file_extents(inode, ordered_extent);