lwip/contrib/ports/unix

This port contains infrastructure and examples for running lwIP on Unix-like
operating systems (Linux, OpenBSD, cygwin). Much of this is targeted towards
testing lwIP applications.

* port/sys_arch.c, port/perf.c, port/include/arch/: Generic platform porting,
  for both states of NO_SYS. (Mapping debugging to printf, providing 
  sys_now & co from the system time etc.)

* check: Runs the unit tests shipped with main lwIP on the Unix port.

* port/netif, port/include/netif: Various network interface implementations and
  their helpers, some explicitly for Unix infrastructure, some generic (but most
  useful on an easy to debug system):

  * fifo: Helper for sio

  * list: Helper for unixif

  * pcapif: Network interface that replays packages from a PCAP dump file, and
    discards packages sent out from it

  * sio: Mapping Unix character devices to lwIP's sio mechanisms

  * tapif: Network interface that is mapped to a tap interface (Unix user
    space layer 2 network device). Uses lwIP threads.