nvme-auth: Don't propose NVME_AUTH_DHGROUP_NULL with SC_C

nvme-auth: Don't propose NVME_AUTH_DHGROUP_NULL with SC_C

Section 8.3.4.5.2 of the NVMe 2.1 base spec states that

"""
The 00h identifier shall not be proposed in an AUTH_Negotiate message
that requests secure channel concatenation (i.e., with the SC_C field
set to a non-zero value).
"""

We need to ensure that we don't set the NVME_AUTH_DHGROUP_NULL idlist if
SC_C is set.

Reviewed-by: Hannes Reinecke <hare@suse.de>
Reviewed-by: Chris Leech <cleech@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Kamaljit Singh <kamaljit.singh@opensource.wdc.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>
Signed-off-by: Keith Busch <kbusch@kernel.org>