This object configures the G.Bond port low downstream rate
crossing alarm threshold. When the current value of
gBondPortStatDnDataRate for this port reaches/drops below or
exceeds this threshold, a gBondLowDnRateCrossing notification
MAY be generated if enabled by
gBondPortConfLowRateCrossingEnable.
This object is read-write for the -O subtype G.Bond ports.
It is irrelevant for the -R subtypes - attempts to read or
change this object for such ports MUST be rejected (in case of
SNMP with the error inconsistentValue).
This object maps to the TR-159 attribute
aGroupThreshDownUpRate.