change-impact example to detect duplicate packets #17

this version of ARP proxy:
https://github.com/tnelson/FlowLog/blob/619e7948b9c37227e396db8c1dcab70b65910a07/interpreter/examples/Arp_Cache_Plus_Macl2.flg

will send a broadcast ARP request even when the original request is for the same IP address as the machine. Now, this may break DNA v4, http://tools.ietf.org/html/rfc4436, but that's a separate problem.

in this version, I tried to squelch those unnecessary broadcasts:
https://github.com/tnelson/FlowLog/blob/72b8b7ba3df0a9f0d3dcfd62a718ced26f4561f2/interpreter/examples/Arp_Cache_Plus_Macl2.flg

but the controller started sending duplicate replies!

this was fixed by this:
https://github.com/tnelson/FlowLog/blob/e3ce9fa497b55860eff53319d47661f6d05a6c1c/interpreter/examples/Arp_Cache_Plus_Macl2.flg