Add QoS backend/rule support table to documentation
Add QoS backend/rule support table to documentation

Added a table in devref documentation to define which
QoS rules are supported by the network backends.

Change-Id: Ie536a05d19cab28eb48bad66b3bc204d017a1ebd

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