The value of tmnxNatGrpCfgSessionWatermarkLo specifies
the low watermark of the number of sessions for each MDA
in this ISA group.
The value of this object must be set together with the value of
tmnxNatGrpCfgSessionWatermarkHi.
The value of this object must be lower than the value of
tmnxNatGrpCfgSessionWatermarkHi, unless both are equal to zero.