MainTab: fix for style of active item underline

[Issue] #1557
[Problem] MainTab: underline for active tab needs update
[Solution]
 - Style of actvie tab has been updated according to guideline

Signed-off-by: Tomasz Lukawski <t.lukawski@samsung.com>

src/css/profile/mobile/common/maintab.less

@@ -46,7 +46,8 @@
 				position: absolute;
 				width: 100%;
 				height: 4 * @px_base;
-				border-bottom: 2.5 * @px_base dotted var(--primary-dark-color);
+				border-bottom: 2.5 * @px_base solid var(--primary-dark-color);
+				border-radius: 1.25 * @px_base;
 				bottom: 0.75 * @px_base;
 				box-sizing: border-box;
 				opacity: 0;