net/mlx5: E-Switch, Fix double allocation of acl flow counter

Flow counter is allocated in eswitch legacy acl setting functions
without checking if already allocated by previous setting. Add a check
to avoid such double allocation.

Fixes: 07bab950 ("net/mlx5: E-Switch, Refactor eswitch ingress acl codes")
Fixes: ea651a86

 ("net/mlx5: E-Switch, Refactor eswitch egress acl codes")
Signed-off-by: Moshe Shemesh <moshe@nvidia.com>
Reviewed-by: Tariq Toukan <tariqt@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>