IB/mlx4: Add receive flow steering support

Implement ib_create_flow() and ib_destroy_flow().

Translate the verbs structures provided by the user to HW structures
and call the MLX4_QP_FLOW_STEERING_ATTACH/DETACH firmware commands.

On the ATTACH command completion, the firmware provides a 64-bit
registration ID, which is placed into struct mlx4_ib_flow that wraps
the instance of struct ib_flow which is retuned to caller.  Later,
this reg ID is used for detaching that flow from the firmware.

Signed-off-by: Hadar Hen Zion <hadarh@mellanox.com>
Signed-off-by: Or Gerlitz <ogerlitz@mellanox.com>
Signed-off-by: Roland Dreier <roland@purestorage.com>