Allow ccndsmoketest to send zero-length datagrams if so instructed.
Allow ccndsmoketest to send zero-length datagrams if so instructed.

cawka/ndnx,cawka/ndnx,svartika/ccnx,svartika/ccnx,ebollens/ccnmp,svartika/ccnx,svartika/ccnx,cawka/ndnx,svartika/ccnx,cawka/ndnx,svartika/ccnx,ebollens/ccnmp,cawka/ndnx,ebollens/ccnmp,ebollens/ccnmp,svartika/ccnx