* rename: `show log dhcp` will become `show log dhcp server`
* add: `show log dhcp client` to display logs from ALL DHCP client processes
* add: `show log dhcp client interface <name>` to display logs from individual DHCP client processes
* add: `show log dhcpv6 server` to display infos about running DHCPv6 server
* add: `show log dhcpv6 client` to display logs from ALL DHCPv6 client processes
* add: `show log dhcpv6 client interface <name>` to display logs from individual DHCPv6 client processes