Listen to mobile data enabled flag change.

The listener is necessary to show/hide the gear icon on top of billing
cycle settings screen as user turn on/off mobile data from QS.

code cleanup: remove dividedCategory

Fix: 28066849
Test: make RunSettinsgRoboTests

Change-Id: I3b7075512042127fd711a8a70a572adfed069502

src/com/android/settings/datausage/BillingCyclePreference.java

@@ -58,8 +58,9 @@ public class BillingCyclePreference extends Preference implements TemplatePrefer
         mSubId = subId;
         mServices = services;
         mPolicy = services.mPolicyEditor.getPolicy(mTemplate);
-        setSummary(getContext().getString(R.string.billing_cycle_fragment_summary,
-                mPolicy != null ? mPolicy.cycleDay : 1));
+        setSummary(getContext().getString(R.string.billing_cycle_fragment_summary, mPolicy != null
+                ? mPolicy.cycleDay
+                : "1"));
         setIntent(getIntent());
     }