SAP: Ensure pending intent is immutable

Bug: 156021269
TAG: #security
Test: manual
Change-Id: Ieea6a708ca0fd1689e4b120db12f0cd96e8db95d
(cherry picked from commit 7b17763dad16814cb743c710efd64cc5fccd2239)
diff --git a/src/com/android/bluetooth/sap/SapServer.java b/src/com/android/bluetooth/sap/SapServer.java
index 69f683f..0ea9575 100644
--- a/src/com/android/bluetooth/sap/SapServer.java
+++ b/src/com/android/bluetooth/sap/SapServer.java
@@ -225,6 +225,7 @@
                 mContext.getString(R.string.bluetooth_sap_notif_title),
                 NotificationManager.IMPORTANCE_HIGH);
         notificationManager.createNotificationChannel(notificationChannel);
+        flags |= PendingIntent.FLAG_IMMUTABLE;
         if (VERBOSE) {
             Log.i(TAG, "setNotification type: " + type);
         }