Add "update_network" implementation to "L3AgentExtension" child classes
Add "update_network" implementation to "L3AgentExtension" child classes

Added "update_network" method implementation to all "L3AgentExtension"
child classes. This new method will be added as a new abstract method
in future neutron-lib releases.

Needed-By: https://review.opendev.org/c/openstack/neutron-lib/+/818536
Related-Bug: #1950454
Change-Id: If319a47e65e4052dd3bbfba700819cbb9183a263

openstack/neutron-vpnaas,openstack/neutron-vpnaas