Change default preload setting to 'Always'.

Also some tidying up to that the default is only specified in a
single place.

Change-Id: I6d66739a8b0d307f8af3c29c62d122a3044c4943
diff --git a/res/xml/bandwidth_preferences.xml b/res/xml/bandwidth_preferences.xml
index 8a31304..f294026 100644
--- a/res/xml/bandwidth_preferences.xml
+++ b/res/xml/bandwidth_preferences.xml
@@ -20,7 +20,7 @@
         android:key="preload_when"
         android:title="@string/pref_data_preload_title"
         android:summary="@string/pref_data_preload_summary"
-        android:defaultValue="@string/pref_data_preload_value_wifi_only"
+        android:defaultValue="@string/pref_data_preload_default_value"
         android:entries="@array/pref_data_preload_choices"
         android:entryValues="@array/pref_data_preload_values"
         android:dialogTitle="@string/pref_data_preload_dialogtitle" />