Update MySQL database schema for DHCPv6 config backend.
This includes 2 MRs: one to align DHCPv4 and DHCPv6 definitions, the second to add missing DHCPv6 stuff, i.e. things added fro DHCPv4 but not yet for DHCPv6.
This includes 2 MRs: one to align DHCPv4 and DHCPv6 definitions, the second to add missing DHCPv6 stuff, i.e. things added fro DHCPv4 but not yet for DHCPv6.