ML2: Lower log level of "Host filtering is disabled" message
ML2: Lower log level of "Host filtering is disabled" message

A warning is too verbose as the situation is normal for
sdn-controller based deployments.

Closes-Bug: #1579286
Change-Id: I972801969424b2fe62b75036bf91bfc6cd56ceb1

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