disable blind subscriber insertion into every VLR/SGSN

During the attempt to fix OS#2785 in Change-Id
I6a92ca34cdaadca9eacc774bb1ca386c325ba865, we introduced logic that
would blindly insert a subscriber *concurrently* in all VLRs/SGSNs of
the network on any update of the subscriber.

Before that patch, we didn't update the current serving SGSN/VLR,
and after the change we created subscribers in all SGSNs/VLRs, of which
all-1 are not serving the subscriber at that time.

We'll have to go back to the original behavior until a proper fix can
be introduced.

Change-Id: Ibf6f1b21b08560d4d8f41bbe7782d40abf4585f8
Related: OS#3091
Related: OS#2785

src/hlr.c

@@ -46,15 +46,18 @@
 static struct hlr *g_hlr;
 
 /* Trigger 'Insert Subscriber Data' messages to all connected GSUP clients.
- *
- * FIXME: In order to support large-scale networks this function should skip
- * VLRs/SGSNs which do not currently serve the subscriber.
  *
  * \param[in] subscr  A subscriber we have new data to send for.
  */
 void
 osmo_hlr_subscriber_update_notify(struct hlr_subscriber *subscr)
 {
+	/* FIXME: the below code can only be re-enabled after we make sure that an ISD
+	 * is only sent tot the currently serving VLR and/or SGSN (if there are any).
+	 * We cannot blindly flood the entire PLMN with this, as it would create subscriber
+	 * state in every VLR/SGSN out there, even those that have never seen the subscriber.
+	 * See https://osmocom.org/issues/3154 for details. */
+#if 0
         struct osmo_gsup_conn *co;
 
 	if (g_hlr->gs == NULL)
@@ -118,6 +121,7 @@ osmo_hlr_subscriber_update_notify(struct hlr_subscriber *subscr)
 			continue;
 		}
 	}
+#endif
 }
 
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