nvme-fabrics: clarify AUTHREQ result handling

The NVMe 2.0 spec defines the ATR and ASCR bits in the AUTHREQ
connect response field to be mutually exclusive. So to clarify the
handling here switch the AUTHREQ handling to use the bit definitions
and check for both bits.
And while we're at it, add a message to the user that secure
concatenation is not supported (yet).

Suggested-by: Mark Lehrer <mark.lehrer@wdc.com>
Signed-off-by: Hannes Reinecke <hare@suse.de>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Signed-off-by: Christoph Hellwig <hch@lst.de>