Set the container field of aconfig flags

Test: m
Bug: 312769710
Change-Id: I1eed7982b40d28947aa3f9575c568eac325dc832

common/FlaggedApi.bp

@@ -17,6 +17,7 @@
 aconfig_declarations {
     name: "com.android.net.flags-aconfig",
     package: "com.android.net.flags",
+    container: "system",
     srcs: ["flags.aconfig"],
     visibility: ["//packages/modules/Connectivity:__subpackages__"],
 }

common/flags.aconfig

@@ -1,4 +1,5 @@
 package: "com.android.net.flags"
+container: "system"
 
 # This file contains aconfig flags for FlaggedAPI annotations
 # Flags used from platform code must be in under frameworks

thread/flags/thread_base.aconfig

@@ -1,4 +1,5 @@
 package: "com.android.net.thread.flags"
+container: "system"
 
 flag {
     name: "thread_enabled"