GGSN_Tests: fix DTE due to passing out-of-bound values to int2oct()

This patch fixes the following DTE happening sporadically:

  04:09:29.373271 mtc GGSN_Tests.ttcn:1478 Dynamic test case error:
    The first argument of function int2oct(), which is 256, does not fit in 1 octet.

Change-Id: I517b8e5d5872c36f7c759433a1cde338c90f16da
1 file changed