net/mlx4_en: Manage flow steering rules with ethtool

Implement the ethtool APIs for attaching L2/L3/L4 based flow steering
rules to the netdevice RX rings. Added set_rxnfc callback and enhanced
the existing get_rxnfc callback.

Signed-off-by: Hadar Hen Zion <hadarh@mellanox.co.il>
Signed-off-by: Amir Vadai <amirv@mellanox.com>
Signed-off-by: Or Gerlitz <ogerlitz@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>