LU-5577 obdclass: (*dt_index_page_build_t) arg nob to size_t

LU-5577 obdclass: (*dt_index_page_build_t) arg nob to size_t

Change the type accordant usage and check for correct input.

Signed-off-by: Dmitry Eremin <dmitry.eremin@intel.com>
Change-Id: Ic80025e95eddbc9fb51efd83c54573e5f310bb0b
Reviewed-on: http://review.whamcloud.com/12382
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: John L. Hammond <john.hammond@intel.com>
Reviewed-by: James Simmons <uja.ornl@gmail.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>