Each row entry in the vRtrPimNgSptSwitchoverThdEntry represents
a group prefix and the corresponding shortest path tree (spt tree)
switchover threshold it has to use.
An entry in this table can be created or destroyed by an SNMP SET
request to vRtrPimNgSptSwovrThdRowStatus. The SET request must
specify the group prefix as well as the threshold, or else the
entry will not be created.