Node.subscribe called more than once behavior undefined

[ReidWilliams]

What API behavior do we want whe user code calls Node.subscribe with an already subscribed peer id but a new callback?

Previous implementation had this:

ids.filter((id) => !this.subscriptions.has(id))
  .forEach((id) => {
    this.subscriptionsManager.subscribe(id, handler)
  })
  .forEach((id) => {
    this.subscriptionsManager.subscribe(id, handler)
  })

This appears to ignore a second call to subscribe for the same peer id.