Replace default route for inet6
Replace default route for inet6

When taking the IPv6 addresses from an interface, also update any routing
table entries.

Change-Id: I0424de6c5c1b0fcb7a9bc3fc1475036668cab09d
Closes-Bug: 1514494

thomasem/devstack,samgoon/devstack,prithivm/branch01,richliu/devstack,mssumanth/devstack,varunarya10/devstack,bswartz/devstack,avvocatodemarchis/devstack,avvocatodemarchis/devstack,openstack-dev/devstack,mssumanth/devstack,noironetworks/devstack,prithivm/branch01,nawawi/openstack,richliu/devstack,dirkmueller/devstack,Mahito/devstack,samgoon/devstack,bswartz/devstack,bigswitch/devstack,dtroyer/devstack,varunarya10/devstack,group-policy/devstack,nawawi/openstack,openstack-dev/devstack,dtroyer/devstack,bigswitch/devstack,dirkmueller/devstack,group-policy/devstack,thomasem/devstack,Mahito/devstack,noironetworks/devstack