xfs: disaggregate xfs_ioctl_setattr

xfs_ioctl_setxflags doesn't need all of the functionailty in
xfs_ioctl_setattr() and now we have separate helper functions that
share the checks and modifications that xfs_ioctl_setxflags
requires. Hence disaggregate it from xfs_ioctl_setattr() to allow
further work to be done on xfs_ioctl_setattr.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Brian Foster <bfoster@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>