[PATCH] Linux: Simplify __opensock and fix race condition [BZ #28353]

[Florian Weimer]

* Adhemerval Zanella:

> Wouldn't be better to move it as the generic implementation (and also cleanup
> it by removing unsualy families like IPX, AX25, and APPLETALK)?

I don't know what Hurd needs, sorry.

I'll post a v2 with the s390 version removed.

Thanks,
Florian