The value of tmnxOamTrProbeHistorySrcNodeId indicates the source
MPLS-TP node identifier of the replying node. The value is copied from
the reply's RFC 6426 Source Identifier TLV. If the TLV is absent, zero
is returned.
This value is relevant when tmnxOamTrCtlTestMode is 'lspTraceRoute' or
'vccvTraceRoute'. Otherwise, zero is returned.