Original problem is that dhcp_release does not work with IPv6, but IPv6
leases still should be released. For example:
1. Start VM in dhcpv6-stateful network, make it acquire IPv6 address.
2. Delete VM.
3. Start another VM in same network before lease expires.
There's a very high chance that the same IPv6 address will be allocated
for both of these VMs (same address will be reused after first VM was
deleted).
On DHCP agent, hosts file would be changed, but not lease file, so
dnsmasq will not give second VM address until lease expires. Reducing
lease time is not a good solution here.
Solution is adding invocation of dhcp_release6 utility when
releasing IPv6 address. dhcp_release6 utility appears in dnsmasq 2.76.
It crafts DHCP6_Release packet, sends it from passed network
interface to IPv6 multicast address and waits for DHCP6_Reply.
Closes-Bug: 1521666
Change-Id: I5efab81cdaf0676503b6c7da0d4b4f400d859286
2aa23de58f