The prefix length associated with the
hpSwitchCosAddressIpv6 object, if an IPv6 CoS
configuration is valid and hpSwitchCosAddressType is
type ipv6. This variable will otherwise be ignored.
The prefix length for an IPv6 entry functions in the
same way as an address mask for an IPv4 entry. The
default value of this object is 128, which specifies
the exact IPv6 address defined in
hpSwitchCosAddressIpv6 (i.e., no subnet-masking is
performed).