xfs: kill xfs_ioctl_setattr behaviour mask

Now there is only one caller to xfs_ioctl_setattr that uses all the
functionality of the function we can kill the behviour mask and
start cleaning up the code.

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