Current count, from CMTS initialization, of unicast granted
minislots on the upstream logical channel, regardless of burst
type. Unicast granted minislots are those in which the CMTS
assigned bandwidth to any unicast SID on the logical channel.
This is the 64 bit version of docsIfCmtsUpChnlCtrUcastGrantedMslots,
and will not be accessible to SNMPv1 managers.
Support for this object is mandatory.