TT#19855 'none' pref enum value must be null

.. to exactly match the old behaviour when
   persisting it.

Change-Id: Ie0b65acfc51ae51001841d9943eee758fac8e73d

db_scripts/diff/15348.down

@@ -0,0 +1,9 @@
+use provisioning;
+set autocommit=0;
+
+set @pid = 0;
+select id into @pid from voip_preferences where attribute = "lock";
+
+update voip_preferences_enum set value = "0" where preference_id = @pid and label = 'none';
+
+commit;

db_scripts/diff/15348.up

@@ -0,0 +1,9 @@
+use provisioning;
+set autocommit=0;
+
+set @pid = 0;
+select id into @pid from voip_preferences where attribute = "lock";
+
+update voip_preferences_enum set value = null where preference_id = @pid and label = 'none';
+
+commit;