NULL packet doesn't need NNN address
NULL packet doesn't need NNN address

Another small annoying change. The NULL packet doesn't need the NNN address
information.

samqixin/ndn-mobility,PhilipsIII/ndn-mobility,shinrs20/ndn-mobility,PhilipsIII/ndn-mobility,shinrs20/ndn-mobility,PhilipsIII/ndn-mobility,shinrs20/ndn-mobility,shinrs20/ndn-mobility,samqixin/ndn-mobility,PhilipsIII/ndn-mobility,PhilipsIII/ndn-mobility,samqixin/ndn-mobility,samqixin/ndn-mobility,shinrs20/ndn-mobility