netifd: rename device section
Rename device section to more user friendly LANX and WAN. This will appear in Ethernet.Interface.{i}.Alias. The value for the parameter Ethernet.Interface.{i}.Name will remain the underlying device name for example, eth0.1, eth1 etc.
Note: for this to take effect, device will need default reset since the change is in uci-defaults and considering this is a cosmetic change, migrations over upgrades is not accounted for.