The value of tmnxSysRollbackStart indicates whether to revert
the rollback file specified by tmnxSysRollbackIndex.
When SET to the value of 'doAction' the system will revert the
rollback file specified by tmnxSysRollbackIndex.
This variable must be set along with tmnxSysRollbackIndex to indicate
the specific rollback file to revert.
An SNMP GET request on this object should return 'notApplicable'.