Changes

msc: do not execute TC_gsup_mt_sms_lu_delay against -latest

This patch fixes regressions in ttcn3-msc-test-latest caused by a
recently merged patch adding MSC_Tests.TC_gsup_mt_sms_lu_delay.

I was expecting it to fail early at this line:

  f_vty_config(MSCVTY, "msc", "timer geran X36 2500"); /* 2.5s */

since timer X36 is not available in the -latest yet.  But this
function executes just fine and the error response is simply ignored.

The -latest version of osmo-msc closes the A-connection early and
then tries to deliver a MT SMS while executing subsequent testcases.

Change-Id: I0b07076a054e30c5a9023de18f2c70f15c97f8cc
Fixes: 8d0d7af2 "msc: add TC_gsup_mt_sms_lu_delay for X36 (LU delay) timer"
Related: SYS#6913