GPRS_Components: use imsi record member

The function f_pcuif_rx_pch_pag_req1 tries to read the IMSI suffix from
the raw data that was exchanged on the PCUIF interface. This is no
longer the appropriate way in PCUIF v.11. There is now a dedicated imsi
member in type record BTS_CCCH_Block, which is used for that purpose.

Related: OS#5927
Change-Id: I0c7c6a31cbf7ed533e665728c157de0ac9e0fe8d
diff --git a/pcu/GPRS_Components.ttcn b/pcu/GPRS_Components.ttcn
index 983ae8f..aaec6d3 100644
--- a/pcu/GPRS_Components.ttcn
+++ b/pcu/GPRS_Components.ttcn
@@ -1175,9 +1175,8 @@
 	rr_pag_req1 := data_msg.rr_msg;
 	log("Rx Paging Request Type1: ", rr_pag_req1);
 
-
-	/* First 3 bytes contain IMSI suffix to calculate paging group: */
-	imsi_suff_octstr := substr(data_msg.raw.data, 0, 3);
+	/* The last 3 digits of the IMSI are used to calculate paging group: */
+	imsi_suff_octstr := substr(char2oct(data_msg.imsi), lengthof(data_msg.imsi) - 3, 3);
 	pag_group_rx := str2int(oct2char(imsi_suff_octstr[0])) * 100 +
 			str2int(oct2char(imsi_suff_octstr[1])) * 10 +
 			str2int(oct2char(imsi_suff_octstr[2]));