nvme_feature_obj has a cdw11 field to store values for set command. but some features are not only take one uint32_t input, but also other data types. such as timestamp, lba range type etc.
for further implements, can we have a void * here? let each feature decide what data structure it should be.

struct nvme_feature_obj {
	void * data;
	nvme_feature_cb	set;
	nvme_feature_cb	get;
	bool namespace_specific;
};