* const'ified olsr_ioctl_{add,del}_route{,6}()

* const'ified olsr_ioctl_{add,del}_route{,6}()
  There are probably a few "const" missing for win32 and BSD.
* const'ified moer parameters in many more functions in the .h and
  .c files
* init-functions with constant or ignored return values are "void"
* created a typedef fro the callback in "struct export_route_entry"
  and using it!
* moved the initilaization of the {add,chg,del}_kernel_list variables
  into process_routes.c. So they are now "static" there.
* olsr_export_{add,del}_route{,6} are now static in process_routes.c
  since they are not used elsewhere.
* olsr_addroute_add_function() and olsr_deldroute_add_function() were
  almost identical - made one function out of it.
  Same for olsr_addroute_del_function() and olsr_deldroute_del_function().
* factored out common code
* fixed the sort order in avl_comp_ipv4_prefix(): We compare now the IPv4
  values in host byte order (and not network byte order). So the route
  list in the e.g. httpinfo plugin is now nicely sorted.