net/mlx5: optimize counter release query generation

net/mlx5: optimize counter release query generation

Query generation was introduced to avoid counter to be reallocated
before the counter statistics be fully updated. Since the counters
be released between query trigger and query handler may miss the
packets arrived in the trigger and handler gap period. In this case,
user can only allocate the counter while pool query_gen is greater
than the counter query_gen + 1 which indicates a new round of query
finished, the statistic is fully updated.

Split the pool query_gen to start_query_gen and end_query_gen helps
to have a better identify for the counter released in the gap period.
And it helps the counter released before query trigger or after query
handler can be reallocated more efficiently.

Signed-off-by: Suanming Mou <suanmingm@mellanox.com>
Acked-by: Matan Azrad <matan@mellanox.com>