Set the container field of aconfig flags

Test: m
Bug: 312769710
Change-Id: I63e922ffcfc96a27e6166252563b3633a5bc0b1a
diff --git a/bluetooth/audio/flags/Android.bp b/bluetooth/audio/flags/Android.bp
index 0d18a4d..c3c8cf5 100644
--- a/bluetooth/audio/flags/Android.bp
+++ b/bluetooth/audio/flags/Android.bp
@@ -1,6 +1,7 @@
 aconfig_declarations {
     name: "btaudiohal_flags",
     package: "com.android.btaudio.hal.flags",
+    container: "system",
     srcs: ["btaudiohal.aconfig"],
 }