Implement ethernet layer send.
Add root CMakeLists.txt
Bind to interface instead of using sendto.

Also stub ethernet receive.
Implement ip_send
Fragment IP packet on send if necessary
Add ip_recv function.

Fix a bug in ip_send. Make example executable much more fun.
Implement checksumming for transport protocols.

Dummy implementation of UDP packet sending.
Change session_open() signature.
Move platform-dependent routines to external.c
Refactor file and function names, includes.

A file corresponding to a given TCP/IP layer now only includes headers
from lower layers.
Basic implementation of the UDP protocol.
Fix UDP-related bugs. Minor format fixes.
Write some TODOs (while I remember).
initial implementation for ICMP/NDP
fix UPD port compare
add previously ommited files
implement simple NDP daemon
reject ip packets which dst_addr doesn't match local_addr