This object indicates the discover mode used by the system to
discover the PD.
A value of 'unknown' indicates that the discover mode on the
interface is unknown.
A value of 'off' indicates that discovery is disabled on the
interface.
A value of 'ieee' indicates that the discover mode on the
interface is IEEE based.
A value of 'cisco' indicates that the discover mode on the
interface is Cisco based.
A value of 'ieeeAndCisco' indicates that the discover mode on
the interface is both IEEE and Cisco based.