xfs: factor out a xfs_attr_match helper

xfs: factor out a xfs_attr_match helper

Source kernel commit: 377f16ac67237c8cda05daf363bcbea95212b000

Factor out a helper that compares an on-disk attr vs the name, length and
flags specified in struct xfs_da_args.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Chandan Rajendra <chandanrlinux@gmail.com>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Eric Sandeen <sandeen@sandeen.net>