Merge updated Ethernet code

Includes the Ethernet communication code itself, as well as integration into the higher level psi46test communication code. 

NOTE: Be sure to set the name of the interface you want to use(eg. eth0) in config.h and give the executable the proper permissions. In linux, this can be done with the command: 

sudo setcap cap_net_raw,cap_net_admin=eip ./bin/psi46test

Also, the pcap library is required for this functionality. It is available in most package repos or can be downloaded from here: http://www.tcpdump.org/#latest-release