Indicates the current loopback state of this interface. The interface
can be in one the following states:
Payload Loopback
Line Loopback
no loopback
Payload or Line loopback modes can be initiated by either of two methods:
Manager requested Loopback (MGRREQPAYLOADLOOP or MGRREQLINELOOP) is
initiated by the Manager of this device.
Network requested Loopback (NETREQPAYLOADLOOP or NETREQLINELOOP) is
initiated by this interface receiving an in-band request on the network
from the far end device.