Bug 2224199

Description of problem:

OVNK ran into an issue while upgrading from non interconnect to interconnect model. During the upgrade as we move to the new zone, new NB and SB dbs are created which will have new UUIDs compared to the older state but the elements are the same (name is the same). Since the UUIDs are different, controller on start up flushes zone 0 which is used by GR's on all nodes in OVNK for doing SNAT. Thus ovn-controller thinks it also owns zone0. On the host, we use zone 0 by default for conntrack and flushing all entries causes outage for existing traffic. One such scenario is:

client (10.0.128.4) is talking to server (10.0.0.5) via GCP load balancer (10.0.0.2 is the VIP that is dnated to 10.0.0.5 - this has NO ovn lb involvement); the server now moves to remote zone, controller on server flushes zone0 which causes entries to be flushed, now if the server is reinitiating the retransmit first it has no idea of history and now creates an entry with srcIP that of 10.0.0.5 and it doesn't know about the older entry 10.0.0.2 which is supposed to be used as the srcIP and this breaks traffic resulting in drop at the server node's interface and after 20-30 seconds of timeout; the client sends the reset which causes the srcPort to change and new traffic to start flowing and only then things settle down. TL;DR flushing zone0 causes traffic outage for 40-50 seconds which is bad.

correct entry before flush: 
tcp 6 431999 ESTABLISHED src=10.0.128.4 dst=10.0.0.2 sport=46122 dport=6443 src=10.0.0.5 dst=10.0.128.4 sport=6443 dport=36363 [ASSURED] mark=0 secctx=system_u:object_r
:unlabeled_t:s0 use=1

bad entry after flush because 10.0.0.5 initiates the connection first: so it thinks its just directly talking to the other node

tcp 6 431999 ESTABLISHED src=10.0.128.4 dst=10.0.0.5 sport=46122 dport=6443 src=10.0.0.5 dst=10.0.128.4 sport=6443 dport=36363 [ASSURED] mark=0 secctx=system_u:object_r
:unlabeled_t:s0 use=1


See previous bug related bug: https://bugzilla.redhat.com/show_bug.cgi?id=2087194

We need to revisit OVN owning the zone0.

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