discovery: Minor refactor

This makes it easier to reinstall discovery's flow from
another component.
dhcpd: Minor refactor

This allows subclasses to more easily override the
addresses that are assigned.
recoco: Change schedule behavior with few tasks

It used to be that when there were only two tasks, we
would just swap between them, ignoring priorities.  We
now actually honor priorities even in this case.
arp_responder: New non-flooding behavior

When arp_responder is being used to fake being a host, you
don't actually want it flooding things theoretically to it.
This adds a "flood" field to the ARP entry so that you can
control it.
misc: Add IP load balancer example

It's a simple IP load balancer that just spreads traffic to one
IP across multiple IPs.