Update cb_cmds with commands to manage global parameters for DHCPv6
First part of CB DHCPv6 work: it will be divided into a premium MR reorganizing code and a second MR adding the DHCPv6 part for global parameters.
First part of CB DHCPv6 work: it will be divided into a premium MR reorganizing code and a second MR adding the DHCPv6 part for global parameters.