gbproxy: Configure a Second SGSN

This adds the required code changes and minimal configuration to both
osmo-gbproxy.cfg and GBProxy_Tests to have osmo-gbproxy connect to two
SGSNs.

No NRI mappings are configured and hence the second SGSN isn't really
used for anything except for bringing the NS-VCs and BVCs up.

Related: OS#4472, SYS#5002
Change-Id: Ib70f7c1a29f089957f882df0e9b05ee526224611
diff --git a/gbproxy/GBProxy_Tests.cfg b/gbproxy/GBProxy_Tests.cfg
index 0e442d1..e1e1eff 100644
--- a/gbproxy/GBProxy_Tests.cfg
+++ b/gbproxy/GBProxy_Tests.cfg
@@ -15,7 +15,10 @@
 GBProxy_Tests.mp_nsconfig_sgsn := {
 	{
 		handle_sns := true
+	}, {
+		handle_sns := true
 	}
+
 }
 
 GBProxy_Tests.mp_nsconfig_pcu := {