[ofw] RE: Ibbus as a filter driver for mthca.

[Hefty, Sean]

>You shouldn't depend on load ordering of filter drivers and instead query for
>the device interface by sending the query interface IRP to the top of the
>driver stack for the current devnode.  You can use IoGetAttachedDeviceReference
>to get the device object at the top of the devnode's driver stack.

The eventual plan is for Winverbs to issue a query interface call to the top of its device stack for the CM interface.  Winmad does something similar for the IBAL MAD interfaces, if you want to look at that as a sample.  The load ordering of the drivers won't matter.

- Sean