generic/009: don't run for btrfs if PAGE_SIZE > 4096

Btrfs has the same issue as XFS here in that the extent layout on a
> 4096 page size system will not match what is reflected in the test
output.

Signed-off-by: Mark Fasheh <mfasheh@suse.de>
Reviewed-by: Eryu Guan <guaneryu@gmail.com>
Signed-off-by: Eryu Guan <guaneryu@gmail.com>