fix: declare DEVICE_CLASS so the Storage tab is reachable

The driver inherits LinuxDriver for the OS surface and set TYPE_LABEL to
"Storage", but netOrk derives device_class from an issubclass chain that
reaches OSDriver before StorageDriver and returned "linux". The UI gates
the Storage tab on device_class === "storage", so an OMV device showed a
Storage label in the list and no Storage tab on the detail page — while
its disks, pools, volumes and shares were being collected and persisted
the whole time.

netOrk now honours an explicit DEVICE_CLASS attribute before falling back
to the chain, mirroring how it already honours TYPE_LABEL.

Refs christianmanivong/netork#111

napalm_openmediavault/openmediavault.py

@@ -49,6 +49,10 @@ class OpenMediaVaultDriver(LinuxDriver):
     """
 
     TYPE_LABEL = "Storage"
+    # Declared outright: the driver inherits LinuxDriver for the OS surface, so
+    # the issubclass chain would otherwise classify an OMV NAS as "linux" and
+    # the UI would never render its Storage tab.
+    DEVICE_CLASS = "storage"
     DRIVER_NAME = "openmediavault"
     driver_name = "openmediavault"
     SSH_FINGERPRINT = [