Set IA background not transparent

The static IA is overlapping the Wi-Fi slice when expanding Wi-Fi slice.
This is caused by that Wi-Fi slice is expanding quickly and static IA
is moving down slowly. We set the background of IA not to transparent
and make IA not overlap slice cards.

Fixes: 129491990
Test: visual
Change-Id: Ib28a18df0016c8fb58bd400085cb658f3bd9d3e6

res/layout/settings_homepage_container.xml

@@ -46,7 +46,8 @@
                 android:id="@+id/main_content"
                 android:layout_width="match_parent"
                 android:layout_height="wrap_content"
-                android:animateLayoutChanges="true"/>
+                android:animateLayoutChanges="true"
+                android:background="?android:attr/windowBackground"/>
 
         </LinearLayout>
     </androidx.core.widget.NestedScrollView>