net/mlx5e: Reuse fold sw stats in representors

Representors software stats are basic, this patch is reusing the
mlx5e_fold_sw_stats in representors, which sums up the basic stats64 for a
mlx5e netdevice.

Fixes: 8bfaf07f ("net/mlx5e: Present SW stats when state is not opened")
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>