The value of tmnxOspfManualSpfTrigger specifies a manual Dijkstra
SPF calculation trigger.
When tmnxOspfManualSpfTrigger is set to 'runTotalSpf' a normal
Dijkstra SPF calculation is performed.
When tmnxOspfManualSpfTrigger is set to 'runExternalsSpf',
only the AS External LSAs are recalculated.
GETs and GETNEXTs on this variable return 'noAction'.