msc: Use random chosen unused local TCP port number for SMPP client

The existing code passed -1 as TCP port number to the SMPP client.
This - very unintuitively - causes TITAN to always chose port number
9999, as that's the default value in IPL4asp.  Let's use '0' instead.

Change-Id: I4db38f4099c388bed23f9a3611619866ede9cbc5
diff --git a/msc/MSC_Tests.ttcn b/msc/MSC_Tests.ttcn
index d59d165..5497c2d 100644
--- a/msc/MSC_Tests.ttcn
+++ b/msc/MSC_Tests.ttcn
@@ -210,7 +210,7 @@
 
 	vc_SMPP := SMPP_Emulation_CT.create(id);
 	map(vc_SMPP:SMPP_PORT, system:SMPP_PORT);
-	vc_SMPP.start(SMPP_Emulation.main_client(pars, mp_msc_ip, mp_msc_smpp_port, "", -1));
+	vc_SMPP.start(SMPP_Emulation.main_client(pars, mp_msc_ip, mp_msc_smpp_port, "", 0));
 }