The table "router_extra_attributes" is a child of "router" table.
Each register contains extra information that completes the router
description. When using ML2/OVS mechanism driver, the methods that
create and populate the "router_extra_attributes" register are always
called from the L3 DVR, L3 HA and availability zones extensions.
When using ML2/OVN, those extensions are not loaded and therefore the
"router_extra_attributes" register is not created.
Despite this register is currently not used in ML2/OVN (it will be in
future features), there are some project expecting the
"router_extra_attributes" register to be always created (for example,
neutron-dynamic-routing [1]).
This patch enforces the child register creating always when a router is
created. This register is populated with the default values. This new
register does not affect any current operation related to ML2/OVN nor
ML2/OVS.
There is a 1:1 relationship between "routers" and
"router_extra_attributes". The child register is deleted by the database
engine when the "routers" register is deleted (ondelete="CASCADE").
[1]https://review.opendev.org/c/openstack/neutron-dynamic-routing/+/863713
Closes-Bug: #1995974
Change-Id: Ic546e40513402fa101c9687acce382cd6b84356c
2081910d6d