gsup: Copy the hlr-Number and use it during purge

Copy the hlr-Number into the sgsn_data and use it during
the purgeMS. There is no unit test that looks at the data
we send so I manually verified this by looking at the output.
Below is the output of the test that purges the subscriber.

<000f> gprs_subscriber.c:170 SUBSCR(123456789012345) Sending GSUP, will send: 0c 01 08 21 43 65 87 09 21 43 f5 09 07 91 83 61 26 31 23 f3
diff --git a/openbsc/src/gprs/gprs_subscriber.c b/openbsc/src/gprs/gprs_subscriber.c
index c2a3ae1..8231e8c 100644
--- a/openbsc/src/gprs/gprs_subscriber.c
+++ b/openbsc/src/gprs/gprs_subscriber.c
@@ -276,6 +276,18 @@
 		}
 	}
 
+	if (gsup_msg->hlr_enc) {
+		if (gsup_msg->hlr_enc_len > sizeof(sdata->hlr)) {
+			LOGP(DGPRS, LOGL_ERROR, "HLR-Number too long (%zu)\n",
+				gsup_msg->hlr_enc_len);
+			sdata->hlr_len = 0;
+		} else {
+			memcpy(sdata->hlr, gsup_msg->hlr_enc,
+				gsup_msg->hlr_enc_len);
+			sdata->hlr_len = gsup_msg->hlr_enc_len;
+		}
+	}
+
 	if (gsup_msg->pdp_info_compl) {
 		rc = gprs_subscr_pdp_data_clear(subscr);
 		if (rc > 0)
@@ -666,11 +678,17 @@
 
 int gprs_subscr_purge(struct gsm_subscriber *subscr)
 {
+	struct sgsn_subscriber_data *sdata = subscr->sgsn_data;
 	struct gprs_gsup_message gsup_msg = {0};
 
 	LOGGSUBSCRP(LOGL_INFO, subscr, "purging MS subscriber\n");
 
 	gsup_msg.message_type = GPRS_GSUP_MSGT_PURGE_MS_REQUEST;
+
+	/* Provide the HLR number in case it is known */
+	gsup_msg.hlr_enc_len = sdata->hlr_len;
+	gsup_msg.hlr_enc = sdata->hlr;
+
 	return gprs_subscr_tx_gsup_message(subscr, &gsup_msg);
 }