net/mlx5: Update last-use statistics for flow rules

Set lastuse statistic, when number of packets is changed compared to
last query. This was wrongly dropped when bulk counter reading was added.

Fixes: a351a1b0 ('net/mlx5: Introduce bulk reading of flow counters')
Signed-off-by: Amir Vadai <amirva@mellanox.com>
Reported-by: Paul Blakey <paulb@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>