Added default data subscription changed callback

Replaced the broadcast intent with the much efficient internal
callback.

Test: Basic telephony functionality tests
Test: atest PhoneSwitcherTest SubscriptionManagerServiceTest
Flag: com.android.internal.telephony.flags.dds_callback
Bug: 353723350
Change-Id: Ib066d0bfe321bd6cf41c9c9b8a6c1d40316a0ed9
diff --git a/flags/data.aconfig b/flags/data.aconfig
index d956104..80d6f61 100644
--- a/flags/data.aconfig
+++ b/flags/data.aconfig
@@ -172,3 +172,13 @@
   description: "Write DataRatStateChanged atom"
   bug:"318519337"
 }
+
+# OWNER=jackyu TARGET=24Q4
+flag {
+  name: "dds_callback"
+  namespace: "telephony"
+  description: "Adding new callback when DDS changed"
+  bug:"353723350"
+}
+
+