The value of tmnxOamTrProbeHistorySrcGlobalId indicates the source
MPLS-TP global 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.