core: use 'normal' value for notification led off

Users can set this value to 250, 500, 1000, 2500 or 5000ms only,
but it's 2000ms by default.

With this patch, 'Normal' string is shown instead of 'By default'
and pulse speed goes to 1 sec.

Change-Id: Idb18ac345bd9eb1a5b795776faa60e2fb5bc258b