btrfs: move btrfs_listxattr prototype to xattr.h

There's a proper header for xattr handlers.
Reviewed-by: Nikolay Borisov <nborisov@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/ctree.h

@@ -3294,9 +3294,6 @@ void __cold btrfs_exit_sysfs(void);
 int btrfs_sysfs_add_mounted(struct btrfs_fs_info *fs_info);
 void btrfs_sysfs_remove_mounted(struct btrfs_fs_info *fs_info);
 
-/* xattr.c */
-ssize_t btrfs_listxattr(struct dentry *dentry, char *buffer, size_t size);
-
 /* super.c */
 int btrfs_parse_options(struct btrfs_fs_info *info, char *options,
 			unsigned long new_flags);

fs/btrfs/xattr.h

@@ -28,6 +28,7 @@ int btrfs_getxattr(struct inode *inode, const char *name,
 int btrfs_setxattr(struct btrfs_trans_handle *trans,
 			    struct inode *inode, const char *name,
 			    const void *value, size_t size, int flags);
+ssize_t btrfs_listxattr(struct dentry *dentry, char *buffer, size_t size);
 
 int btrfs_xattr_security_init(struct btrfs_trans_handle *trans,
 				     struct inode *inode, struct inode *dir,