[ofw] crash on IBBUS disabling while mad traffic

[Hefty, Sean]

>Adding winverbs.sys back into the driver stack and running the WDTF test
>'Disable_Enable_With_IO.wsf', I now see random crashes:
>  1) write to read-only memory in ibbus.sys - bus_pnp.c: al_deref_ifc(), refcnt
>decr blew-up as memory had been released.
>  2) Driver corrupted pool in svr.sys
>  3) driver corrupted pool in mrxsmb.sys

I think I see the reason for the winverbs issue.  It releases the CM interface once per device, rather than just once total.