MSC_Tests.ttcn: introduce TC_gsup_mt_multi_part_sms

The idea of this test case is to verify the process of multi-part
MT SMS transmission. The MSC should keep the RAN connection until
the last message part is transmitted.

Change-Id: I6308586a70c4fb3254c519330a61a9667372149f
Related: OS#3587
diff --git a/msc/expected-results.xml b/msc/expected-results.xml
index 7a35296..8a19d5b 100644
--- a/msc/expected-results.xml
+++ b/msc/expected-results.xml
@@ -67,6 +67,7 @@
   <testcase classname='MSC_Tests' name='TC_gsup_mo_smma' time='MASKED'/>
   <testcase classname='MSC_Tests' name='TC_gsup_mt_sms_ack' time='MASKED'/>
   <testcase classname='MSC_Tests' name='TC_gsup_mt_sms_err' time='MASKED'/>
+  <testcase classname='MSC_Tests' name='TC_gsup_mt_multi_part_sms' time='MASKED'/>
   <testcase classname='MSC_Tests' name='TC_lu_and_mo_ussd_single_request' time='MASKED'/>
   <testcase classname='MSC_Tests' name='TC_lu_and_mt_ussd_notification' time='MASKED'/>
   <testcase classname='MSC_Tests' name='TC_lu_and_mo_ussd_during_mt_call' time='MASKED'/>