Description of problem:
while start a ipv6 virtual network, there will have a new virtual interface created in the pysical host which got a globel ipv6 address from the ipv6 network, however, the virtual interface won't got a link local address like fe80 address automatically, this will lead the guest fail to bind the ipv6 network during we start the guest which graphical buffer bind to ipv6 network

Version-Release number of selected component (if applicable):
libvirt-1.2.17-13.el7.x86_64

How reproducible:
100%

Steps to Reproduce:
1.Prepare a xml for ipv6 network
#cat ipv6-net.xml
<network ipv6='yes'>
  <name>ipv6-net</name>
  <uuid>7ba66277-91b2-45b0-810b-f3620b924790</uuid>
  <forward mode='nat'/>
  <bridge name='virbr6' stp='on' delay='0'/>
  <mac address='52:54:00:46:07:af'/>
  <ip family='ipv6' address='2001:b8:ca2:2::1' prefix='64'>
    <dhcp>
      <range start='2001:b8:ca2:2:1::10' end='2001:b8:ca2:2:1::ff'/>
    </dhcp>
  </ip>
</network>


2.Define the network and start it, after start it, we could find the a new virtual interface created in the physcial host, however the interface have no linklocal address(fe80 address) assigned
#virsh define ipv6.xml
# virsh net-start ipv6-net
Network ipv6-net started

# ifconfifg
--

virbr6: flags=4099<UP,BROADCAST,MULTICAST>  mtu 1500
        inet6 2001:b8:ca2:2::1  prefixlen 64  scopeid 0x0<global>
        ether 52:54:00:46:07:af  txqueuelen 0  (Ethernet)
        RX packets 0  bytes 0 (0.0 B)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 0  bytes 0 (0.0 B)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

3.Start a guest which graphical buffer listen on ipv6 network, guest will fail to start since failed to initialize spice server

#virsh dumpxml rhel72
--
    <graphics type='spice' autoport='yes'>
      <listen type='network' network='ipv6-net'/>
    </graphics>

# virsh start rhel72
error: Failed to start domain rhel72
error: internal error: process exited while connecting to monitor: ((null):21135): Spice-Warning **: reds.c:3107:reds_init_socket: reds_init_socket: binding socket to 2001:b8:ca2:2::1:5900 failed
2015-10-15T09:24:31.904199Z qemu-kvm: failed to initialize spice server

Actual results:
Fail to start guest while the guest's graphical buffer bind to ipv6 network

Expected results:
1.if we could implement this new function that assign a fe80 link address to the virtual interface automatically, then we hope fix it, since it's a very useful function for the guest's graphics 

2.if we could't support it, please record it in doc, so that it won't confuse the consumer 

Additional info:
File this bug during review the following bug
https://bugzilla.redhat.com/show_bug.cgi?id=1192318