Use flags.aconfig in platform for android networking

flags.aconfig for android networking is under
packages/modules/Connectivity.
But, currently, mainline code should not read trunk stable flag.
To avoid confusion, this CL moves flags.aconfig to platform.

Bug: 315302281
Test: TH
Change-Id: I7142d937a59a880b68c11fff9254c84b39ce072f
diff --git a/AconfigFlags.bp b/AconfigFlags.bp
index 08961ed..654b08f 100644
--- a/AconfigFlags.bp
+++ b/AconfigFlags.bp
@@ -657,7 +657,13 @@
     defaults: ["framework-minus-apex-aconfig-java-defaults"],
 }
 
-// CoreNetworking
+// Networking
+aconfig_declarations {
+    name: "com.android.net.flags-aconfig",
+    package: "com.android.net.flags",
+    srcs: ["core/java/android/net/flags.aconfig"],
+}
+
 java_aconfig_library {
     name: "com.android.net.flags-aconfig-java",
     aconfig_declarations: "com.android.net.flags-aconfig",