Add additional SIOC* socket ioctl constants from linux/sockios.h on
Linux.

Change-Id: I76f8c9d9d0015d398ee52844b3c9f506cd182329
Reviewed-on: https://go-review.googlesource.com/47950Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>