Correct link in config-ml2.rst
Correct link in config-ml2.rst

Change-Id: If52835c2fcdb2391fff986dc1fbcc04da0815ff6
Closes-Bug: #1727941

eayunstack/neutron,openstack/neutron,eayunstack/neutron,huntxu/neutron,noironetworks/neutron,huntxu/neutron,openstack/neutron,noironetworks/neutron,mahak/neutron,openstack/neutron,mahak/neutron,mahak/neutron