Singular prefix ownership mode

[rcgoodfellow]

Consider adding a flag that enforces singular prefix ownership. In this mode when a Maghemite routing daemon receives a prefix advertisement, it checks the underlying platform for other routes to that prefix. If such routes exist and they were not put there by the Maghemite routing daemon, they will be removed by Maghemite. This can be helpful in ensuring that the Maghemite daemon has complete control over its prefixes. It can also be helpful in crash recovery if prefix nexthops change between crashes.

[rcgoodfellow]

For this to be robust, we'd also need to monitor the underlying platform for route updates.

[rcgoodfellow]

This just destroyed half my day. When a new switch zone comes up in a development environment, the link locals can get renumbered. If you do this a bunch, you wind up with a large pile of stale routes from Omicron installs gone by. This leads to massive route flapping.