Represents the reason for tunnel down.
The following values are supported:
tunnelTimeout - When AC detects the tunnel is broken,
- it will notify NMS.
keyUpdateFailure - rekey process is failed, tunnel will be broken.
apReset - Administrator reset AP.
apCrash - AP reboot for system crash.
apDeleted - Delete AP from AC and trigger tunnel down.
apCfgChange - The configuration for AP was changed.