nvmet: Make cntlid globally unique

We usually log the cntlid which is confusing in case
we have multiple subsystems each with it's own cntlid ida.
Instead make cntlid ida globally unique and log the initial
association.

Signed-off-by: Sagi Grimberg <sagi@grimberg.me>
Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>
Reviewed-by: Max Gurtovoy <maxg@mellanox.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@fb.com>