the ability to optionally associate packet to tx queue

right now for an app, you may be processing packets for a great many logical streams where for each stream it needs to output to the same tx queue to preserve order but to scale would want to spread out the streams across queues. This isn’t currently possible in capsule. Not sure the best api for this.

No files or tests are named. Start by examining capsule's packet transmission and tx queue entry points, then determine how an optional stream-to-queue association can preserve per-stream ordering while distributing streams across queues. Done means the API and behavior for this association are defined and implemented.

Written by the indexing model from the issue text.