Partial IP/UDP/CoAP implementation
Test case for UDP; doesn't work yet correctly
Basic UDP test cases works.  Still very much WIP.
Additional skeleton, refactored udp input to eth input
More progress
Add more printing to mockup_CoAP_get
ICMP echo now works
Fix bugs in ethernet and udp.  UDP & CoAP now work.
Add ARP and refactor
Fix UDP payload length & CoAP reply code