The default document icon (a white document) is displayed in Network Connections when the network adapter has a LAN media type but has no sub-media type. The sub-media type defines the medium of the adapter: 1394, TVC, LAN, Wireless, WWAN or Bluetooth.
There is an expectation,but not a requirement, that all LAN network adapters specify one of the sub-media types. When the network adapter has no sub-media type, Windows defaults to using the document icon for the network adapter.
The issue is purely cosmetic. There is no issue with the operation of the network adapter.