In case when physical bridge is removed and created again it
is initialized by neutron-ovs-agent.
But if agent has enabled distributed routing, dvr related
flows wasn't configured again and that lead to connectivity issues
in case of DVR routers.
This patch fixes it by adding configuration of dvr related flows
if distributed routing is enabled in agent's configuration.
It also adds reset list of phys_brs in dvr_agent. Without that there
were different objects used in ovs agent and dvr_agent classes thus
e.g. 2 various cookie ids were set on flows in physical bridge.
This was also the same issue in case when openvswitch was restarted and
all bridges were reconfigured.
Now in such case there is correctly new cookie_id configured for all
flows.
Change-Id: I710f00f0f542bcf7fa2fc60800797b90f9f77e14
Closes-Bug: #1864822
91f0bf3c85