[dhcp6] enable DHCP6 server and client for reference device (#646)
[dhcp6] enable DHCP6 server and client for reference device (#646)


openthread/ot-br-posix,bukepo/borderrouter,openthread/borderrouter,openthread/ot-br-posix,openthread/ot-br-posix,openthread/ot-br-posix,openthread/borderrouter,openthread/borderrouter,openthread/borderrouter,bukepo/borderrouter,bukepo/borderrouter,bukepo/borderrouter,openthread/borderrouter,bukepo/borderrouter,openthread/ot-br-posix,openthread/borderrouter,openthread/ot-br-posix