Add 'search' glyphicon to filter panel header

netbox/templates/ipam/prefix_list.html

@@ -26,6 +26,7 @@
 	<div class="col-md-3">
 		<div class="panel panel-default">
 			<div class="panel-heading">
+				<span class="glyphicon glyphicon-search" aria-hidden="true"></span> 
 				<strong>Search</strong>
 			</div>
 			<div class="panel-body">