getDeviceData do not detect vlan for my Cat4000 switches running CatOS version 8.4.1.

This case turned out to be a bit complicated, however, the root cause is that the device reports identical serials for its three modules. I have now added support to getDeviceData for detecting this case, and handling it by ignoring any duplicate serials. Hopefully the VLANs will how up on this device now.

-- Kristian