sgsn: Introduce test TC_attach_echo_timeout

This test verifies sgsn drops all GGSN related pdp context when that
GGSN stops answering echo requests.

Change-Id: Ic31748924e7bf05ea2ccf2b1be0c460eefed5782
diff --git a/sgsn/expected-results.xml b/sgsn/expected-results.xml
index d9c3706..fc8856a 100644
--- a/sgsn/expected-results.xml
+++ b/sgsn/expected-results.xml
@@ -54,6 +54,7 @@
       SGSN_Tests.ttcn:MASKED TC_attach_second_attempt testcase
     </failure>
   </testcase>
+  <testcase classname='SGSN_Tests' name='TC_attach_echo_timeout' time='MASKED'/>
   <testcase classname='SGSN_Tests' name='TC_attach_restart_ctr_echo' time='MASKED'/>
   <testcase classname='SGSN_Tests' name='TC_attach_restart_ctr_create' time='MASKED'/>
   <testcase classname='SGSN_Tests' name='TC_attach_pdp_act_deact_mt_t3395_expire' time='MASKED'/>