xfs: allow setting file attributes on special files

XFS does't have file attributes manipulation ioctls for special
files. Changing or reading file attributes is rejected for them in
xfs_fileattr_*et().

In XFS, this is necessary to work for project quota directories.
When project is set up, xfs_quota opens and calls FS_IOC_SETFSXATTR on
every inode in the directory. However, special files are skipped due to
open() returning a special inode for them. So, they don't even get to
this check.

The recently added file_getattr/file_setattr will call xfs_fileattr_*et,
on special files. This patch allows reading/changing file attributes on
special files.

Signed-off-by: Andrey Albershteyn <aalbersh@redhat.com>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Carlos Maiolino <cem@kernel.org>