- Use RTF_PROTO2 for routes handled by RIPng and ignore the other

- Use RTF_PROTO2 for routes handled by RIPng and ignore the other
  routes.

  The route6d depends on RTF_WASCLONED to prevent connected
  network routes (normally configured automatically when ifconfig
  assigns an address with a prefix) from being removed.  However,
  that flag is no longer used on 8.0 and later due to lltable
  rework.  The route6d now sees routes with RTF_PROTO2 only.

  The flag can be changed by the -Q <num> flag.  The default is
  2.

- -Q and -P now allow the value "0".  It clears the flag itself.