net/mlx5e: Add ethtool flow steering support

Implement etrhtool set_rxnfc callback to support ethtool flow spec
direct steering. This patch adds only the support of ether flow type
spec. L3/L4 flow specs support will be added in downstream patches.

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>