buf_ring in HEAD is racy

[Ryan Stone]

On Sat, Dec 14, 2013 at 7:06 PM, Adrian Chadd <adrian at freebsd.org> wrote:
> oh cool, you just did the output-drops thing I was about to code up.
> We're missing those counters at work and the ops guys poked me about
> it.
>
> I'll also give that a whirl locally and see about working with jack to
> get it into -HEAD / MFC'ed to 10.
>
> Thanks!

The reason why I call it hacky is because these drops are properly
categorized as discards, not errors.  But there's not currently a
really good way to distinguish between the two in FreeBSD right now
(there is the drops counter in the if_snd queue but netstat seemed to
be ignoring that even with -d specified and blindly overwriting it
would seem to be incompatible with altq anyway)