This object indicates the method of discovery used
by the system for the detection of the Powered Device(PD).
A value of unknown(0) means that the discovery method
is unknown on this port.
A value of off(1) means that the discovery method
is turned off on this port.
A value of ieee(2) indicates that the discovery method
is IEEE based on this port.
A value of cisco(3) indicates that the discovery method
is Cisco based on this port.