db v5: prep for D-GSM: add vlr_via_proxy and sgsn_via_proxy

D-GSM will store in the HLR DB whether a locally connected MSC has attached the
subscriber (last_lu_seen[_ps]), or whether the attach happened via a GSUP proxy
from a different site.

Add columns for this separately in this patch.

Change-Id: I98c7b3870559ede84adf56e4bf111f53c7487745
diff --git a/sql/hlr.sql b/sql/hlr.sql
index ad57661..98e586d 100644
--- a/sql/hlr.sql
+++ b/sql/hlr.sql
@@ -43,7 +43,12 @@
 	-- Timestamp of last location update seen from subscriber
 	-- The value is a string which encodes a UTC timestamp in granularity of seconds.
 	last_lu_seen TIMESTAMP default NULL,
-	last_lu_seen_ps TIMESTAMP default NULL
+	last_lu_seen_ps TIMESTAMP default NULL,
+
+	-- When a LU was received via a proxy, that proxy's hlr_number is stored here,
+	-- while vlr_number reflects the MSC on the far side of that proxy.
+	vlr_via_proxy	VARCHAR,
+	sgsn_via_proxy	VARCHAR
 );
 
 CREATE TABLE subscriber_apn (
@@ -78,4 +83,4 @@
 
 -- Set HLR database schema version number
 -- Note: This constant is currently duplicated in src/db.c and must be kept in sync!
-PRAGMA user_version = 4;
+PRAGMA user_version = 5;