net/mlx5e: Add support to get ethtool flow rules

Enhance the existing get_rxnfc callback:
1. Get flow rule of specific ID.
2. Get all flow rules.
3. Get number of rules.

Signed-off-by: Maor Gottlieb <maorg@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>