Add scrollview for dns dialog

Also update dialog to appcompat to avoid the crash

Change-Id: Ide6483f1160713dae8111de533a8b3345a3420c2
Fixes: 111351793
Test: Manual

res/layout/private_dns_mode_dialog.xml

@@ -14,8 +14,12 @@
      limitations under the License.
 -->
 
-<LinearLayout
+<ScrollView
     xmlns:android="http://schemas.android.com/apk/res/android"
+    android:layout_width="match_parent"
+    android:layout_height="wrap_content">
+
+    <LinearLayout
         android:layout_width="match_parent"
         android:layout_height="wrap_content"
         android:orientation="vertical"
@@ -71,4 +75,7 @@
             android:minHeight="48dp"
             android:paddingStart="16dp"
             android:textAppearance="?android:attr/textAppearanceSmall"/>
-</LinearLayout>
+    </LinearLayout>
+
+</ScrollView>
+