dhcp: fix unicast pkts, clean up state machine

dhcp: fix unicast pkts, clean up state machine

Send dhcp unicast packets to ip4-lookup. Otherwise, these packets
won't reach a dhcp server on a different subnet.

Do an immediate client scan after processing wakeup events.

Calculate the next process wakeup time by scanning all
clients.

Increase maximum (idle, no-clients-configured) timeout to 1000
seconds.

Reduce log spew.

Type: fix

Signed-off-by: Dave Barach <dave@barachs.net>
Change-Id: I3d10cd4c353298ed0b19e7e30887dc1d8d07b19e
(cherry picked from commit c54162981cdd41d65ed283df36955007552ddffe)