Fix DVR to service LBaaS VIP Ports

Fix DVR to service LBaaS VIP Ports

Currently, DVR router namespaces are created only
when there is a valid VM port on the compute
node, or for the gateway-port on the service node.
But when an LBaaS VIP port is created the l3 agent
does not create a DVR namespace to service the VIP port.
This fix enables DVR namespaces to be created to
service the LBaaS VIP port.

Also, this fix enables L2 Agent running in DVR
mode, to add-in OVS rules to enable packets to
be routed to such LBaaS VIP Ports which are
resident on DVR routed interfaces.

Therefore, with this fix both East-West and
North-South traffic will be serviced by DVR
for LBaas VIP Ports.

DocImpact

Authored-by: Swaminathan Vasudevan <swaminathan.vasudevan@hp.com>
Co-Authored-By: Vivekanandan Narasimhan <vivekanandan.narasimhan@hp.com>
Change-Id: I698b971d50721fb0512a11569f7d3139d0d456f3
Closes-Bug: #1356464