MAC, IPv4, IPv6 changes in the Ryu's Packet library

They are not automatically translated into human readable format anymore , as this was introducing a lot of overhead.

http://www.mail-archive.com/ryu-devel@lists.sourceforge.net/msg04213.html

Now Ryu has comparable performance against dpkt. It is only 15~20% slower on unpacking, and 2 times slower on packing a packet. ( Down from 500% and 700% )