net/sched: act_ct: update nf_conn_acct for act_ct SW offload in flowtable

When the act_ct SW offload in flowtable, The counter of the conntrack
entry will never update. So update the nf_conn_acct conuter in act_ct
flowtable software offload.

Signed-off-by: wenxu <wenxu@ucloud.cn>
Reviewed-by: Roi Dayan <roid@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>