[GAR] Set selectable attribute to W+ network preference

[Root Cause]
The Preference defautl is clickable. So if the preference is only to
display information to user. Need to set the attribute to false.

Bug: 187442654
Test: Manual test
Change-Id: I8a9c3156e3166db3043cca521f28489b4bd3e89f

res/xml/mobile_network_settings.xml

@@ -85,7 +85,8 @@
 
         <Preference
             android:key="carrier_wifi_network"
-            android:title="@string/carrier_wifi_network_title"/>
+            android:title="@string/carrier_wifi_network_title"
+            android:selectable="false"/>
 
         <SwitchPreference
             android:key="mms_message"