[ofw] help deciphering mlx4 driver

[Hefty, Sean]

>ca_event_handler is never invoked.
>My oversight, thank you.
>But do you really need it ?
>MTHCA *does* call ca_event_handler, but it is not used by IBAL.

I'm trying to have the mlx4 driver report asynchronous events to anyone that subscribes for them.  Basically, this allows the HCA driver to support multiple consumers of asynchronous events, i.e. both IBAL and Winverbs, and allows the eventually elimination of the overhead of using an intermediate driver to invoke callbacks.

If you can point me to where the IBAL async callback is invoked, I can modify the code there instead.

- Sean