sgsn: Add test to verify duplicate DeactPDPCtx crashing osmo-sgsn

osmo-sgsn sends 2 DeletePdpCtxReq on gtp, Confirmation received on first
one frees cbp associatd to pdp and the second one accesses the already
freed cbp.

Related: OS#3956
Change-Id: Ie1cc9fdf91b18b0b7fb3d5fb33b6dcf6f46a393f
diff --git a/sgsn/expected-results.xml b/sgsn/expected-results.xml
index 0b477d1..d9c3706 100644
--- a/sgsn/expected-results.xml
+++ b/sgsn/expected-results.xml
@@ -47,6 +47,7 @@
   <testcase classname='SGSN_Tests' name='TC_attach_pdp_act_ggsn_reject' time='MASKED'/>
   <testcase classname='SGSN_Tests' name='TC_attach_pdp_act_user_deact_mo' time='MASKED'/>
   <testcase classname='SGSN_Tests' name='TC_attach_pdp_act_user_deact_mt' time='MASKED'/>
+  <testcase classname='SGSN_Tests' name='TC_attach_pdp_act_deact_dup' time='MASKED'/>
   <testcase classname='SGSN_Tests' name='TC_attach_second_attempt' time='MASKED'>
     <failure type='fail-verdict'>Tguard timeout
       SGSN_Tests.ttcn:MASKED SGSN_Tests control part