xfs: reject invalid flags combinations in XFS_IOC_ATTRMULTI_BY_HANDLE

While the flags field in the ABI and the on-disk format allows for
multiple namespace flags, that is a logically invalid combination that
scrub complains about.  Reject it at the ioctl level, as all other
interface already get this right at higher levels.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>