[openib-general] ipoib multicast timeouts

[Sean Hefty]

> 1. Do not migrate ipoib to use the multicast module.
> 2. Add a timeout to the multicast module.  It's not clear how to reconcile
> different timeouts for the same group, so I'm less certain how to do this.
> 3. Currently, ipoib backoff is used both as the timeout for a single request and
> the time between retries.  Instead, use it only the time between retrying
> requests.

After studying ipoib more, I'm leaning strongly towards option 1 at this point. 
  I don't think that ipoib would benefit from using the multicast module, nor do 
I think it would it simplify the code any.

- Sean