dhcp: fix crash on unicast renewal send

dhcp: fix crash on unicast renewal send

Type: fix

- when the addresses were learnt a copy of the client was sent to the
main thread, this meant the unicast adjacecny was saved on the copy
not on the original.
- Add logging.
- Improve the proxy-node that hands the clint packets so the DHCP
packets are traced.
 - allow a renewal to configure new address data

Change-Id: I6ab0afcccbc4a1cdefdd1b8beeda8fc7ba20ec1f
Signed-off-by: Neale Ranns <nranns@cisco.com>