[ofw] crash in mlx4 driver

[Sean Hefty]

>I've added this field (p_hca_obj) for WinVerbs, because it needs it now
>for performing QueryCa.
>Before that WinVerbs was using p_hca_dev field, which was wrong, because
>this field contains HCA's PDO.

As Fab pointed out, the field had a dual use.  It was set to the HCA object (and
not the PDO), when responding to the query interface call.  (Path of minimal
change.)

>In fact, WinVerbs can perform QueryCa using the existing interface like
>IBAL does.
>If Sean will change WinVerbs to do that, he can remove this field as
>unnecessary.

I'm not following this.  I defined the RDMA_INTERFACE_VERBS structure for
winverbs.  What do you mean by 'perform QueryCa'?  Do you mean obtain this
interface?

Now that IBAL is in the same device stack as the HCA, does it need the PDO
exchanged through the ci_interface_t?

My preference is to undo the change to struct RDMA_INTERFACE_VERBS, but if it
must be kept for some reason, then at the very least the GUID should be updated.
This would cause incompatible builds of the drivers to fail to obtain the
interfaces.

- Sean