extensions: libxt_quota: Allow setting the remaining quota

extensions: libxt_quota: Allow setting the remaining quota

The current xt_quota module cannot track the current remaining quota
of a specific rule. Everytime an unrelated rule is updated in the same
iptables table, the quota will be reset. This is not a very useful
function for iptables that get changed at run time. This patch fixes the
above problem by adding a new field in the struct that records the
current remaining quota.

Fixed a print out bug in verbose print out wrt. inversion.

Signed-off-by: Chenbo Feng <fengc@google.com>
Suggested-by: Maciej Żenczykowski <maze@google.com>
Reviewed-by: Maciej Żenczykowski <maze@google.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>