The value of the object tmnxDhcpSvrSubnetMinFree specifies
the desired minimum number of free addresses in this subnet.
The actual number of free addresses in this subnet is indicated in the
column tmnxDhcpSvrSubnetStatsFree in the augmentation row
of the tmnxDhcpSvrSubnetStatsTable.
If the actual number of free addresses in this subnet falls below
this configured minimum, a notification is generated.
The value zero specifies 'no minimum'.