[PATCH v2 3/7] nvme: update nvme_id_ns OPTPERF constants

[Christoph Hellwig]

> In NVMe verson 2.0 and below, OPTPERF comprises only bit 4 of NSFEAT in
> the Identify Namespace structure. Since version 2.1, OPTPERF includes
> both bits 4 and 5 of NSFEAT. Replace the NVME_NS_FEAT_IO_OPT constant
> with NVME_NS_FEAT_OPTPERF_SHIFT, NVME_NS_FEAT_OPTPERF_MASK, and
> NVME_NS_FEAT_OPTPERF_MASK_2_1, representing the first bit, pre-2.1 bit
> width, and post-2.1 bit width of OPTPERF.

Please add this in a comment in the code.