MFC r351028: Report NOIOB and NPWG fields as stripe size.

Namespace Optimal I/O Boundary field added in NVMe 1.3 and Namespace
Preferred Write Granularity added in 1.4 allow upper layers to align
I/Os for improved SSD performance and endurance.

I don't have hardware reportig those yet, but NPWG could probably be
reported by bhyve.

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