xfs: revert 1baa2800e62d ("xfs: remove the unused XFS_ALLOC_USERDATA flag")

Revert this commit, as it caused periodic regressions in xfs/173 w/
1k blocks.

[1] https://lore.kernel.org/lkml/20190919014602.GN15734@shao2-debian/

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Brian Foster <bfoster@redhat.com>
2 files changed