Support Deactivate PDP Context Request from network

Enable Deactivate PDP context based on the IMSI of the subscriber.
When there are PDP contexts present for a MM context,
PDP context will be deactivated along with GMM Detach(MM context deletion).
If there are no PDP present, MM context will be deleted to avoid
further PDP context request from the MS.
Test cases is added to check this functionality.

Change-Id: Ia0a41aa2218ec2fda4ea17a37c8cc55cba63dd13
diff --git a/openbsc/tests/sgsn/sgsn_test.ok b/openbsc/tests/sgsn/sgsn_test.ok
index c7a53b9..c36b643 100644
--- a/openbsc/tests/sgsn/sgsn_test.ok
+++ b/openbsc/tests/sgsn/sgsn_test.ok
@@ -34,4 +34,8 @@
   - RA Update Request (RA 2 -> RA 2)
 Testing APN matching
 Testing GGSN selection
+Testing pdp deactivation
+Testing Pdp deactivation for MS with pdp ctx
+Testing Pdp deactivation for MS without MM ctx
+Testing Pdp deactivation for MS with only MM ctx
 Done