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
diff --git a/lib/neutron-legacy b/lib/neutron-legacy
index c244e54..2c0c9cf 100644
--- a/lib/neutron-legacy
+++ b/lib/neutron-legacy
@@ -799,7 +799,7 @@
         local IP_ADD=""
         local IP_DEL=""
         local DEFAULT_ROUTE_GW
-        DEFAULT_ROUTE_GW=$(ip r | awk "/default.+$from_intf/ { print \$3; exit }")
+        DEFAULT_ROUTE_GW=$(ip -f $af r | awk "/default.+$from_intf/ { print \$3; exit }")
         local ADD_OVS_PORT=""
 
         if [[ $af == "inet" ]]; then
@@ -811,7 +811,7 @@
         fi
 
         if [ "$DEFAULT_ROUTE_GW" != "" ]; then
-            ADD_DEFAULT_ROUTE="sudo ip r replace default via $DEFAULT_ROUTE_GW dev $to_intf"
+            ADD_DEFAULT_ROUTE="sudo ip -f $af r replace default via $DEFAULT_ROUTE_GW dev $to_intf"
         fi
 
         if [[ "$add_ovs_port" == "True" ]]; then