bhyve: abort and return FEATURE_NOT_SAVEABLE while set feature with a save flag for NVMe controller.
Currently bhyve's NVMe controller cannot save feature values cross
reboot. It should return a FEATURE_NOT_SAVEABLE error when the command
specifies a save flag.
If the Feature Identifier specified in the Set Features command is not
saveable by the controller and the controller receives a Set Features
command with the Save bit set to one, then the command shall be aborted
with a status of Feature Identifier Not Saveable.