Using stateless NAT in OVN should always be a better choice for FIPs
because it allows to avoid hitting conntrack, potentially improving
NAT performance, esp. where hardware offload for the openflow rules is
involved.
The only limitation for using stateless NAT in OVN is that it requires
1:1 IP mapping; which is always the case for FIPs. This is why this
patch unconditionally switches to stateless for all FIPs.
Before setting stateless key to NAT's options, check that 'options'
are supported. (Support was added in OVN 20.03 as part of stateless
NAT implementation.) If an older OVN version is used, nothing changes.
The patch also adds a runtime migration rule for neutron-server to
transform all existing stateful fips to stateless.
Change-Id: I312a950131d62d93fb4bc121bc5e60febb8d35ee
dc677682ca