Set the container field of aconfig flags

Test: m
Bug: 312769710
Change-Id: I1eed7982b40d28947aa3f9575c568eac325dc832
diff --git a/common/flags.aconfig b/common/flags.aconfig
index 8eb3cbf..30f5d9c 100644
--- a/common/flags.aconfig
+++ b/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