nvme: add comment for unaligned "fake" nqn

Current "fake" nqn field is "nqn.2014.08.org.nvmexpress:", it is
not aligned with the canonical version for history reasons.
Signed-off-by: Linjun Bao <meljbao@gmail.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>

drivers/nvme/host/core.c

@@ -2704,7 +2704,11 @@ static void nvme_init_subnqn(struct nvme_subsystem *subsys, struct nvme_ctrl *ct
 			dev_warn(ctrl->device, "missing or invalid SUBNQN field.\n");
 	}
 
-	/* Generate a "fake" NQN per Figure 254 in NVMe 1.3 + ECN 001 */
+	/*
+	 * Generate a "fake" NQN similar to the one in Section 4.5 of the NVMe
+	 * Base Specification 2.0.  It is slightly different from the format
+	 * specified there due to historic reasons, and we can't change it now.
+	 */
 	off = snprintf(subsys->subnqn, NVMF_NQN_SIZE,
 			"nqn.2014.08.org.nvmexpress:%04x%04x",
 			le16_to_cpu(id->vid), le16_to_cpu(id->ssvid));