It can be hard to track where references are taken and released.

In networking, we have annoying issues at device or netns dismantles,
and we had various proposals to ease root causing them.

This patch adds new infrastructure pairing refcount increases
and decreases. This will self document code, because programmers
will have to associate increments/decrements.

This is controled by CONFIG_REF_TRACKER which can be selected
by users of this feature.

This adds both cpu and memory costs, and thus should probably be
used with care.
Signed-off-by: NEric Dumazet <edumazet@google.com>
Reviewed-by: NDmitry Vyukov <dvyukov@google.com>
Signed-off-by: NJakub Kicinski <kuba@kernel.org>