write useful comments

db_scripts/diff/13042.up

@@ -10,11 +10,11 @@ DELETE a.* FROM voip_usr_preferences a, voip_usr_preferences b
   WHERE a.subscriber_id=b.subscriber_id
   AND a.attribute_id=@old_nur_id AND b.attribute_id=@old_aur_id;
 
+-- finally copy over the vars to the new preference
 INSERT INTO voip_usr_preferences(subscriber_id, attribute_id, value) 
   SELECT p.subscriber_id, @new_pref_id, "never" from voip_usr_preferences p
   WHERE p.attribute_id=@old_nur_id;
 
--- finally copy over the vars to the new preference
 INSERT INTO voip_usr_preferences(subscriber_id, attribute_id, value) 
   SELECT p.subscriber_id, @new_pref_id, "ice_strip_candidates" from voip_usr_preferences p
   WHERE p.attribute_id=@old_aur_id;
@@ -24,10 +24,12 @@ SELECT id FROM voip_preferences WHERE attribute='always_use_ipv4_for_rtpproxy' I
 SELECT id FROM voip_preferences WHERE attribute='always_use_ipv6_for_rtpproxy' INTO @old_pref_v6_id;
 SELECT id FROM voip_preferences WHERE attribute='ipv46_for_rtpproxy' INTO @new_pref_id;
 
+-- delete logically conflicting rows - ipv4 takes precedence
 DELETE a.* FROM voip_usr_preferences a, voip_usr_preferences b
   WHERE a.subscriber_id=b.subscriber_id
   AND a.attribute_id=@old_pref_v6_id AND b.attribute_id=@old_pref_v4_id;
 
+-- finally copy over the vars to the new preference
 INSERT INTO voip_usr_preferences(subscriber_id, attribute_id, value) 
   SELECT p.subscriber_id, @new_pref_id, "force_ipv4" from voip_usr_preferences p
   WHERE p.attribute_id=@old_pref_v4_id;