rework the ICMP6 decoder:

rework the ICMP6 decoder:
  -replace private flag printers and replace them with bittok2str()
  -remove some flesh from inline printf() statements make more use of tok2str()
  -option printer gets a multiline output (behind vflag)
   -context hexdump for options
  -replace some u_int32 with u_int8[4] to get around compiler padding issues