FS_IOC_SETFLAGS ioctl should return EOPNOTSUPP if the file attribute
(e.g. FS_NOCOW_FL) is not supported, rather than silently ignoring it
and returning success.
Fixes: 9b1bb01c8ae7 (f2fs: convert to fileattr)
Signed-off-by: Harry Austen <harryausten@xxxxxxxxxxxxx>