Add apex_available field in networkstack-aidl-interfaces am: 49d1392e am: 5510d18e am: 263b5816

Original change: https://googleplex-android-review.googlesource.com/c/platform/packages/modules/NetworkStack/+/11360536

Change-Id: I237fa7af18334cf0ebf2ac1b07e5c3ae7a5979df