This object identifies the type of address carried in
cmplsTeP2mpTunnelDestSrcSubGroupOrigin.
Since the object cmplsTeP2mpTunnelDestSrcSubGroupOrigin must
conform to the protocol specification, this object must
return either ipv4(1) or ipv6(2) at a transit or egress LSR.
At an ingress LSR, there is no source sub-group and this
object should return the value unknown(0).