Mark the EntitlementManager PendingIntents as immutable.

These are read-only intents and should not be mutated by any
app receiving them.

Bug: 178324405
Bug: 178249531
Test: atest TetheringTests TetheringCoverageTests GtsTetheringTestCases
Change-Id: I5395e7c19e6453640ad790f2b9a9ba22bbcefa88

Tethering/src/com/android/networkstack/tethering/EntitlementManager.java

@@ -418,7 +418,8 @@ public class EntitlementManager {
             if (period <= 0) return;
 
             Intent intent = new Intent(ACTION_PROVISIONING_ALARM);
-            mProvisioningRecheckAlarm = PendingIntent.getBroadcast(mContext, 0, intent, 0);
+            mProvisioningRecheckAlarm = PendingIntent.getBroadcast(mContext, 0, intent,
+                    PendingIntent.FLAG_IMMUTABLE);
             AlarmManager alarmManager = (AlarmManager) mContext.getSystemService(
                     Context.ALARM_SERVICE);
             long periodMs = period * MS_PER_HOUR;