Set to tenMbps(1) to operate in 10Mbps speed mode. Set to
oneHundredMbps(2) to operate in 100Mbps speed mode. Set to
autoNegotiate(3) to allow the switch to negotiate the operating
speed with the other end of the connection.
If the value of object cssSwitchPortType is WS-X4002(2),
this object will be read-only, because FX module only
supports 100Mbps speed.