Add container to .aconfig

Change-Id: Ia3c4b59363d46a64c9329dd39cbcfee6113d329e
Test: m
Bug: 328444881
diff --git a/services/usb/Android.bp b/services/usb/Android.bp
index e8ffe54..e00627e 100644
--- a/services/usb/Android.bp
+++ b/services/usb/Android.bp
@@ -44,6 +44,7 @@
 aconfig_declarations {
     name: "usb_flags",
     package: "com.android.server.usb.flags",
+    container: "system",
     srcs: ["**/usb_flags.aconfig"],
 }