PGW_Tests: refactor/improve several parameters to accomodate for different GTPv2C interfaces

So far we were only testing s5/s8 interface, but we'll want to test s2b
soon.
This commit is a mixture of refactorings and code improvements as a step
towards testing S2b interface.

Change-Id: I22b3e18d02ca828e2ea43bde2e0a602db236cf50
diff --git a/library/GTPv2_Templates.ttcn b/library/GTPv2_Templates.ttcn
index 8df234a..431415a 100644
--- a/library/GTPv2_Templates.ttcn
+++ b/library/GTPv2_Templates.ttcn
@@ -887,13 +887,14 @@
 			  template (value) octetstring apn, template (value) BIT3 pdn_type,
 			  template (omit) FullyQualifiedTEID_List teid_list,
 			  template (value) OCT2 chg_car, template (value) uint4_t bearer_id,
+			  template (omit) UserLocationInfo uli := omit,
 			  template (value) Bearer_QoS qos := ts_GTP2C_BearerQos('09'O, 0,0,0,0)) :=
 ts_PDU_GTP2C('00000000'O, '000000'O, '20'O, {
 	createSessionRequest := {
 		iMSI := ts_GTP2C_Imsi(imsi),
 		mSISDN := fs_GTP2C_msisdn(msisdn),
 		mEI := omit,
-		userLocationInfo := omit,
+		userLocationInfo := uli,
 		servingNetwork := omit,
 		rAT_Type := ts_GTP2C_RatType(rat_type),
 		indication := omit,