system_routing_configure should not delete and re-add all routes
Currently system_routing_configure will blow away all routes and then re-add them. In environments with a lot of static routes, it can take a little time to re-add them. For example with about 50 routes, there will be about 2 seconds where routes are missing between them being deleted and added back. This causes a brief outage for anything that requires static routes when making changes in the web interface, and wiping out all the routes is unnecessary.
Possible solution, rather than deleting all routes, first check to see if the same route still exists, and if it does, don't delete it. i.e. only delete routes that are going to get deleted anyway.
Ticket #507. Do not remove all static routes to readd them back. The change will never delete a rule but define the action to be taken on it, either add or change a present route. Be consinstent on gateways allowed to be selected as destinations for static routes, including dynamic gateways.
Do not unconditionaly remove the default route and readd it. This should make system_routing_configure more
reliably. Ticket #507