Switch ports 0..3 are connected to external ports LAN{1..4} in sequence,
switch port 4 is not used, and switch port 5 is connected to the CPU.
The WAN port is attached to the CPU's second network interface; it has no
connection to the internal switch.
Reuse the "Dell TrueMobile 2300" entry, which describes the same mapping.
Signed-off-by: Mirko Parthey <mirko.parthey@web.de>