Extend accounting capabilities to support quotas

The accounting framework already supports accounting at the
quota and byte level.  As such it is a natural extention to
add a ceiling limit to those metrics.

Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
src: fix broken output handling

In 948fa3b ("Extend accounting capabilities to support quotas"), the
error handling of snprintf is incorrect since this function may
return -1 on error. Add a new SNPRINTF_CHECK() macro to offload the
complicated handling of snprintf.

Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>