menu: reduce the vertical padding beween elements by half

Doing tab conversion makes the space waste more obvious than ever.
Try to close the gap a little, open for discussion!

src/opnsense/www/themes/opnsense/assets/stylesheets/bootstrap/_list-group.scss

@@ -21,7 +21,7 @@
 .list-group-item {
   position: relative;
   display: block;
-  padding: 12px 20px;
+  padding: 6px 20px;
   // Place the border on the list items and negative margin up for better styling
   margin-bottom: -1px;
   background-color: $list-group-bg;

src/opnsense/www/themes/opnsense/build/css/main.css

@@ -4311,7 +4311,7 @@ a.thumbnail.active {
 .list-group-item {
   position: relative;
   display: block;
-  padding: 12px 20px;
+  padding: 6px 20px;
   margin-bottom: -1px;
   background-color: #fff; }
   .list-group-item:last-child {