Small fix for Linux __opensock

[Wolfram Gloger]

> There is a good reason for the current order but I cannot remember
> right now.  I'll have to think more about it.

It's certainly possible that the current order in __opensock has other
advantages.  Let me know and I will try to come up with a more
specific workaround for if_nameindex(), since I doubt that we can get
unix_ioctl() in Linux-2.2 and earlier changed.

Regards,
Wolfram.