nvmet: demote discovery cmd parse err msg to debug

Host can send invalid commands and flood the target with error messages
for the discovery controller. Demote the error message from pr_err() to
pr_debug( in nvmet_parse_discovery_cmd(). 
Signed-off-by: NChaitanya Kulkarni <chaitanya.kulkarni@wdc.com>
Signed-off-by: NChristoph Hellwig <hch@lst.de>

drivers/nvme/target/discovery.c

@@ -379,7 +379,7 @@ u16 nvmet_parse_discovery_cmd(struct nvmet_req *req)
 		req->execute = nvmet_execute_disc_identify;
 		return 0;
 	default:
-		pr_err("unhandled cmd %d\n", cmd->common.opcode);
+		pr_debug("unhandled cmd %d\n", cmd->common.opcode);
 		req->error_loc = offsetof(struct nvme_common_command, opcode);
 		return NVME_SC_INVALID_OPCODE | NVME_SC_DNR;
 	}