NLSR

Currently Sync does not do anything to handle NACKs. Since NLSR is using a forked version of Sync, we are not in a position to refactor it heavily to do so. However, we should refactor Sync to process them minimally by logging the NACK and its context, i.e. the function name that was executing, the logical "task" we were in, etc., so that we can understand the kind of NACK behavior that Sync is producing.