CacheFiles: Handle rename2

Not all filesystems now provide the rename i_op - ext4 for one - but rather
provide the rename2 i_op.  CacheFiles checks that the filesystem has rename
and so will reject ext4 now with EPERM:

	CacheFiles: Failed to register: -1

Fix this by checking for rename2 as an alternative.  The call to vfs_rename()
actually handles selection of the appropriate function, so we needn't worry
about that.

Turning on debugging shows:

	[cachef] ==> cachefiles_get_directory(,,cache)
	[cachef] subdir -> ffff88000b22b778 positive
	[cachef] <== cachefiles_get_directory() = -1 [check]

where -1 is EPERM.
Signed-off-by: David Howells <dhowells@redhat.com>

fs/cachefiles/namei.c

@@ -779,7 +779,8 @@ struct dentry *cachefiles_get_directory(struct cachefiles_cache *cache,
 	    !subdir->d_inode->i_op->lookup ||
 	    !subdir->d_inode->i_op->mkdir ||
 	    !subdir->d_inode->i_op->create ||
-	    !subdir->d_inode->i_op->rename ||
+	    (!subdir->d_inode->i_op->rename &&
+	     !subdir->d_inode->i_op->rename2) ||
 	    !subdir->d_inode->i_op->rmdir ||
 	    !subdir->d_inode->i_op->unlink)
 		goto check_error;