The value of tmnxOamPingHistorySrcGlobalId 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 tmnxOamPingCtlTestMode is 'lspPing' or
'vccvPing'. Otherwise, zero is returned.