picotcp barebox integration

[Antony Pavlov]

Hi!

I have just published latest picotcp-enabled barebox.
Please see my picotcp.20150331 branch in my github barebox repo
(https://github.com/frantony/barebox/tree/picotcp.20150331).

This version is based on latest barebox-next and latest picotcp-development.
Here is barebox picotcp network features:

       * network interfaces and the 'ifconfig' command to rule them;
       * the 'route' command to see current picotcp route table;
       * the 'picoping' command to use picotcp ping support (also now barebox responds
         to ping requests);
       * the 'dhclient' command to use picotcp dhcp client;
(new)  * picotcp-based tftp filesystem support.


Here is note/todo list:

  1. tftp write operation is not supported;

  2. with picotcp we can't easely use 'tftp' command with old syntax
     (no $<current ethernet>.serverip anymore);

  3. just now picotcp-based tftp file transfer is 5 times slower than
     old realisation (partialy it is my bad, e.g. extra memory copy operation
     is used for code simplification);

  4. picotcp has dns support, but just now it is unused in barebox;
 
  5. no nfs support in picotcp (should we can keep current barebox nfs support on
     top of barebox UDP support?).

-- 
Best regards,
  Antony Pavlov