sgsn: Avoid race condition in TC_suspend_rau()

In f_routing_area_update() we are sending a RAU Complete to the SGSN
and then immediately afterwards send a GTP-U from the simulated
GGSN to the SGSN.  That GTP might reach the SGSN faster than the
RAU Complete, resulting in a test failure.

Change-Id: Ic489e0857115cf24965e413a39918edc5a8f44f8

sgsn/SGSN_Tests.ttcn

@@ -3105,6 +3105,9 @@ private function f_TC_suspend_rau(charstring id) runs on BSSGP_ConnHdlr {
 	/* perform RAU (implicit RESUME) */
 	f_routing_area_update(g_pars.ra);
 
+	/* give SGSN some time to actually receve + process the RAU Complete we sent */
+	f_sleep(0.5);
+
 	/* now data should be flowing again */
 	f_gtpu_xceive_mt(apars, f_rnd_octstring(100));