Description of problem:
metadata- enable_isolated_metadata = True: After attaching network to router and restarting dhcp agent, static route is not removed from /var/lib/neutron/NID/opts

Version-Release number of selected component (if applicable):
[root@overcloud-controller-2 ~]# rpm -qa | grep neutr
openstack-neutron-common-7.0.1-10.el7ost.noarch
openstack-neutron-ml2-7.0.1-10.el7ost.noarch
openstack-neutron-openvswitch-7.0.1-10.el7ost.noarch
python-neutron-lbaas-7.0.0-2.el7ost.noarch
openstack-neutron-7.0.1-10.el7ost.noarch
openstack-neutron-metering-agent-7.0.1-10.el7ost.noarch
python-neutron-7.0.1-10.el7ost.noarch
openstack-neutron-lbaas-7.0.0-2.el7ost.noarch
python-neutronclient-3.1.0-1.el7ost.noarch


How reproducible:
100%

Steps to Reproduce:
1. Configure  enable_isolated_metadata = True in /etc/neutron/dhcp-agent.ini
2. Create Internal net and subnet. 
3. See there is a static route to 169.254.169.254 in dhcp options- 
cat /var/lib/neutron/dhcp/107277c1-ba33-4e50-93b2-750c8bc594a6/opts
tag:tag0,option:dns-server,10.35.28.28
tag:tag0,option:classless-static-route,169.254.169.254/32,192.168.2.1,0.0.0.0/0,192.168.2.1
tag:tag0,249,169.254.169.254/32,192.168.2.1,0.0.0.0/0,192.168.2.1
tag:tag0,option:router,192.168.2.1

4. Create a router. Attach network port to a router. Restart dhcp agent. 


Actual results:
the static route to 169.254.169.254 still exists

Expected results:
the static route to 169.254.169.254 should be removed. 


Additional info:
All extra info will be added when requested