[PATCH 9/9] nvme: add support for streams and directives

[Christoph Hellwig]

Looks mostly good,

but two nit-picks:

 - can we keep a module option to disable streams, or in fact for
   now maybe to explicitly enable it?  I expect this to be interesting
   at least for the first devices that implement it.  Also given that
   it needs to be explicitly enabled I would expect some overhead of
   just enabling it when never used
 - do we even need the < 4 streams fallback now that they are global
   instead of per-ns instead of just disabling the feature for now?