[PATCH v2] nvme: update keep alive interval when kato is modified

[hch at lst.de]

Any reason we can't just call this from nvme_passthru_end instead
of inventing a new API?  Right now the nvmet passthrough code never
uses the underlying keep alive code, so it doesn't make a difference,
but I expect we'll need more handling for passthrough commands like
this, and we might also grow more users (e.g. the io_uring based
passthrough).