net/mlx4_en: Add support for drop action through ethtool

The drop action is implemented by allocating a QP and keeping it in a reset state
such that the HW drops any packets which are steered to that QP. When a drop action
is requested, we attach the relevant flow to that QP.

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