[MINOR] stick-table: use suffix "_cnt" for cumulated counts

[MINOR] stick-table: use suffix "_cnt" for cumulated counts

The "_cnt" suffix is already used by ACLs to count various data,
so it makes sense to use the same one in "conn_cnt" instead of
"conn_cum" to count cumulated connections.

This is not a problem because no version was emitted with those
keywords.

Thus we'll try to stick to the following rules :

  xxxx_cnt : cumulated event count for criterion xxxx
  xxxx_cur : current number of concurrent entries for criterion xxxx
  xxxx_rate: event rate for criterion xxxx