nvmet: mask pending AENs

Per section 5.2 of the NVMe 1.3 spec:

  "When the controller posts a completion queue entry for an outstanding
  Asynchronous Event Request command and thus reports an asynchronous
  event, subsequent events of that event type are automatically masked by
  the controller until the host clears that event. An event is cleared by
  reading the log page associated with that event using the Get Log Page
  command (see section 5.14)."

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
diff --git a/drivers/nvme/target/nvmet.h b/drivers/nvme/target/nvmet.h
index f4d16d9..480dfe1 100644
--- a/drivers/nvme/target/nvmet.h
+++ b/drivers/nvme/target/nvmet.h
@@ -139,6 +139,7 @@ struct nvmet_ctrl {
 	u32			kato;
 
 	u32			aen_enabled;
+	unsigned long		aen_masked;
 	struct nvmet_req	*async_event_cmds[NVMET_ASYNC_EVENTS];
 	unsigned int		nr_async_event_cmds;
 	struct list_head	async_events;