-*- Mode: Outline -*-* Before release:** Implement flags support in changeif.c and options.c** Fix and move if_index.c to libinetutils.** Port to BSD.** Make sure it is a drop in replacement at least for the most   common options on Linux and BSD.* Some systems can provide more interfaces than  SIOCGIFCONF/if_nameindex, interfaces which are usually not UP but  registered nevertheless.  (linux: /prov/net/dev). Some support for that?* Honour IFF_CANTCHANGE when working in flag setting in brdaddr,  dstaddr, etc.* We could put the option parsing (invocation of getopt_long) into a  function like parse_opt_rest, which could be used by  system_parse_opt_rest to continue parsing the options as usual after  processing a non-option.* Is it necessary to merge long/short options intelligently?  For example, if a system specific option shadows a normal option?  Allow this?