freebsd patch from Enrico Tassi

freebsd patch from Enrico Tassi

  * ifdata:
    - Use unsigned long for ioctl command.
      On both Linux and FreeBSD ioctl expects an unsigned long command.
      FreeBSD kernel was complaining about the (by chance) signedness of
      the ioctl command (then probably ignored, since it worked both on
      Linux and FreeBSD).

        WARNING pid 799 (ifdata): ioctl sign-extension ioctl ffffffffc0206933

    - put #if defined(__linux__) around ioctls that are not supported by
      FreeBSD

    - Mention in the manpage that some options are Linux specific.