net/sched: TC, fix raw counter initialization

Freed counters may be reused by fs core.
As such, raw counters may not be initialized to zero.

Cache the counter values when the action stats object is initialized to
have a proper base value for calculating the difference from the previous
query.

Fixes: 2b68d659 ("net/mlx5e: TC, support per action stats")
Signed-off-by: Oz Shlomo <ozsh@nvidia.com>
Reviewed-by: Paul Blakey <paulb@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>