This object indicates the status of the Link Test function
for the port. Set to false indicates valid data or 4
consecutive Link Test pulses have been detected on the
port. Set to true indicates the failure of the Link Test
function for the port. In the Link Test Fail state, data
transmission, data reception and collision detection functions
are disabled until valid data or 4 consecutive Link Test pulses
appear on the RXD+/- pair of the port.