Update if.h to match Linux kernel headers?

[Florian Weimer]

On 06/17/2016 11:12 AM, Joseph Myers wrote:
> On Thu, 16 Jun 2016, Carlos O'Donell wrote:
>
>> I'm not entirely sure if userspace can make use of these flags, but one
>> could conceivably write userspace tools and drivers that would.
>
> In <https://sourceware.org/ml/libc-alpha/2014-06/msg00413.html> I noted
> that I presumed the exclusion of IFF_* values not fitting in a "short"
> flags field was deliberate.

Can you elaborate way?  Do you fear that we might end up with an ABI 
change if the enum promotes to int, not short?  But doesn't do it that 
already, due to the value IFF_DYNAMIC = 0x8000?

Thanks,
Florian