reorder: fix unit test for random starting point

reorder: fix unit test for random starting point

The reorder library unit test was performed under the assumption that
the start sequence number was always 0.
This is not the case anymore as the start sequence number is initialized
by the first packet inserted into the reorder buffer.

This patch updates the unit test to reflect the new behavior.

Fixes: 7e1fa1de8a53 ("reorder: allow random number as starting point")

Reported-by: Mukesh Dua <mukesh.dua81@gmail.com>
Signed-off-by: Reshma Pattan <reshma.pattan@intel.com>
Acked-by: Sergio Gonzalez Monroy <sergio.gonzalez.monroy@intel.com>