This devref is covering the existing OpenStack-Helm neutron
architecture and proposal for introducing multiple SDNs.
Added linuxbridge usage docs.
Change-Id: If6c8753d85ea2bd2fd7df77e84b5e61bf64dc507
Implements: blueprint support-linux-bridge-on-neutron
Co-Authored-By: Gage Hugo <gagehugo@gmail.com>