The user-specified port group for which the settings are
defined. This value MAY have meaning to the user for the
purposes of identifying groups of dot1dBridge ports with
similar function (uplink, user, etc).
A value of zero(0) has special meaning in that it identifies
the default port grouping of characteristics present in the
agent. Entries indexed by a zero have a max-access of
read-only. This value will have a system defined maximum of
etsysCosIrlPortGroupMaxEntries.