The length of the Prefix associated with cswmFlowQueryGroup.
When the 'groupmask' bit of cswmFlowQueryMask object in the
same row is on, an appropriate value should be specified and
only rows with the specied group address prefix will be
returned in the result table. If the 'groupmask' bit in the
associated cswmFlowQueryMask is off, this object is ignored
during the query.
A value of zero causes all addresses to match.
This prefix length will be consistent with the type specified in
cswmFlowQueryAddrType.