From: Hannes Reinecke <hare@xxxxxxxxxx>
A failure in nvmet_setup_auth() does not mean that the NVMe
authentication command failed, so we should rather return a protocol
error with a 'failure1' response than an NVMe status.
Also update the type used for dhchap_step and dhchap_status to u8 to
avoid confusions with nvme status. Furthermore, split dhchap_status and
nvme status so we don't accidentally mix these return values.