Add IMMUTABLE flag to IKE PendingIntent

To follow the newly added requirement that enforces PendingIntent
to have an explicit mutability flag on creation

Bug: 176900430
Test: FrameworksIkeTests. CtsIkeTestCases
Change-Id: Ibdade3710411f0102699692ac61bd387a07956be
diff --git a/src/java/com/android/internal/net/ipsec/ike/IkeSessionStateMachine.java b/src/java/com/android/internal/net/ipsec/ike/IkeSessionStateMachine.java
index c3c648d..132c519 100644
--- a/src/java/com/android/internal/net/ipsec/ike/IkeSessionStateMachine.java
+++ b/src/java/com/android/internal/net/ipsec/ike/IkeSessionStateMachine.java
@@ -1491,7 +1491,7 @@
         intent.putExtras(bundle);
 
         return PendingIntent.getBroadcast(
-                context, 0 /*requestCode unused*/, intent, 0 /*default flags*/);
+                context, 0 /* requestCode; unused */, intent, PendingIntent.FLAG_IMMUTABLE);
     }
 
     /**