LibVirt: Disable hairpin when using Neutron

When hairpinning is enabled, ICMPv6 messages that handle
duplicate address detections return to the instance, causing IPv6
SLAAC configuration to fail

http://tools.ietf.org/html/rfc4862#section-5.4.3

Closes-Bug: #1251235

Change-Id: I65e1d40d33d6291bfd5558c7c346fc5fbf92cc56
Merge "LibVirt: Disable hairpin when using Neutron"