MT#64020 fix 15797 to avoid restoring valid peer prefs

* this fix addresses voip_peer_preferences default values
  restoration in 15797 and it from now on only restores missing
  default values for preferences that do not have peer_pref
  with non default value NULL, so that scenarios where a
  preference does not exists in voip_peer_preference because
  it was manually selected by the customer with the value NULL
  so it does not exists in voip_peer_preferences for that reason.

Change-Id: I83ee3294cab896679575187066a3960818dc2f77

db_scripts/diff/15797.up

@@ -48,4 +48,11 @@ SELECT ph.id, p.id, pe.value
   JOIN voip_peer_hosts ph
   LEFT OUTER JOIN voip_peer_preferences pp ON pp.attribute_id = p.id AND ph.id = pp.peer_host_id
  WHERE p.peer_pref = 1 AND pe.peer_pref = 1 AND pe.default_val = 1 AND pe.value IS NOT NULL
-   AND pp.value IS NULL;
+   AND pp.value IS NULL
+   AND NOT EXISTS (
+    SELECT id FROM voip_preferences_enum pn
+    WHERE pn.preference_id = p.id
+      AND pn.peer_pref = 1
+      AND pn.default_val = 0
+      AND pn.value IS NULL
+    LIMIT 1);