Ipv6 server creation failure with v6-fixed option

When Ipv6 instance is created using the v6-fixed ip option,

the server goes to error state.

To Reproduce the bug:

Create a network:
network create net1 --provider-network-type vxlan

Create a subnet:
subnet create --ip-version=6 --ipv6-address-mode=slaac --ipv6-ra-mode=slaac --network net1 --subnet-range 2001:db8:cafe:e::/64 sub1

Create a router:
router create router1

Add interface to the router:
router add subnet router1 sub1

Create a server:
server create --image <imageID> --flavor m1.tiny --nic net-id=net1, v6-fixed-ip=2001:db8:cafe:e:f816:3eff:fea1:e170 VM1

Also, add fixed-ip option when used after creating the server , it doesnt get the fixed ip.The ip gets auto assigned or sometimes both the ip's are assigned.

a.Create Network
network create net2 --provider-network-type vxlan
b. Create subnet
subnet create --ip-version=6 --no-dhcp --network net6 --subnet-range 2006:db9:cafe:e::/64 sub6

c. Create Server:
server create --image cirros --flavor cirros --nic net-id=net6 vm1

d.server add fixed-ip
server add fixed ip vm1 2006:db9:cafe:e::8