epdg: Tx Service-Selection in s6b AAR msg

This AVP is actually mandatory as per Table 9.1.2.2.1 in TS 29.273.

Change-Id: I86d01a0f5148e98b7faebbe0e3d7617a6c90b559
diff --git a/library/DIAMETER_ts29_273_Templates.ttcn b/library/DIAMETER_ts29_273_Templates.ttcn
index 3daf299..38355e7 100644
--- a/library/DIAMETER_ts29_273_Templates.ttcn
+++ b/library/DIAMETER_ts29_273_Templates.ttcn
@@ -207,6 +207,7 @@
 template (value) PDU_DIAMETER
 ts_DIA_S6b_AAR(template (value) hexstring imsi,
 	       template (value) MIPv6_NONE_MIP6_Feature_Vector mip6_feat_vec,
+	       template (value) charstring apn,
 	       template (value) octetstring sess_id := c_def_sess_id,
 	       template (value) charstring orig_host := "pgw.localdomain",
 	       template (value) charstring orig_realm := "localdomain",
@@ -227,7 +228,8 @@
 			ts_AVP_DestinationRealm(dest_realm),
 			ts_AVP_AuthRequestType(AUTHORIZE_ONLY),
 			ts_AVP_UserNameImsi(valueof(imsi)),
-			ts_AVP_MIP6FeatureVector(mip6_feat_vec)
+			ts_AVP_MIP6FeatureVector(mip6_feat_vec),
+			ts_AVP_ServiceSelection(valueof(apn))
 			/* TODO: Lots other optional */
 	});