Add controller's scenario for flow mod that changes ipv6 dst address

It turned out that the bug is no longer present. To check this start the switch with two ports (tap0 and tap1) and run the controller with the ipv6_change_dst scenario. Then use tcpreplay to send pcap.data/icmp_v6.pcap to tap0 interface and check that the dst ipv6 address is changed on the outgoing interface (tap1).