Btrfs: Make ACLs return EOPNOTSUPP for now

There was a slight problem with ACL's returning EINVAL when you tried to set an
ACL.  This isn't correct, we should be returning EOPNOTSUPP, so I did a very
ugly thing and just commented everybody out and made them return EOPNOTSUPP.
This is only temporary, I'm going back to implement ACL's, but Chris wants to
push out a release so this will suffice for now.

Also Yan suggested setting reada to -1 in the delete case to enable backwards
readahead, and in the listxattr case I moved path->reada = 2; to after the if
(!path) check so we can avoid a possible null dereference.  Thank you,

Signed-off-by: Chris Mason <chris.mason@oracle.com>
diff --git a/fs/btrfs/xattr.c b/fs/btrfs/xattr.c
index f4ac5e0..984616c 100644
--- a/fs/btrfs/xattr.c
+++ b/fs/btrfs/xattr.c
@@ -302,9 +302,9 @@
 	key.offset = 0;
 
 	path = btrfs_alloc_path();
-	path->reada = 2;
 	if (!path)
 		return -ENOMEM;
+	path->reada = 2;
 
 	mutex_lock(&root->fs_info->fs_mutex);
 
@@ -410,7 +410,7 @@
 	path = btrfs_alloc_path();
 	if (!path)
 		return -ENOMEM;
-
+	path->reada = -1;
 	key.objectid = inode->i_ino;
 	btrfs_set_key_type(&key, BTRFS_XATTR_ITEM_KEY);
 	key.offset = (u64)-1;