netfilter: nfnetlink_acct: dump unmodified nfacct flags

NFNL_MSG_ACCT_GET_CTRZERO modifies dumped flags, in this case
client see unmodified (uncleared) counter value and cleared
overquota state - end user doesn't know anything about overquota state,
unless end user subscribed on overquota report.

Signed-off-by: Alexey Perevalov <a.perevalov@samsung.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>