switch block layer polling to a bio based model v4

[Christoph Hellwig]

On Tue, Oct 12, 2021 at 05:57:43PM +0300, Sagi Grimberg wrote:
> Jens, is that with nvme_core.multipath=Y ?

That is the default.  But for most PCI device namespaces are private
by default so we won't use the multipath code anyway.  Only for
dual ported devices, and even for those that flag might need to be set
explicitly at namespace creation time.