net/mlx5: Introduce software defined steering capabilities

There are two different internal steering modes, abstracted from the
rest of the driver. In order to keep upper layer of the driver agnostic
to the differences in capabilities of the steering modes, this patch
introduces mlx5_fs_get_capabilities() API to check if a certain software
defined capability is supported. It differs from the capabilities
exposed by the hardware, as it takes into account the flow steering mode
(SMFS/DMFS) currently enabled.

This implementation supports only two capability flags:

  MLX5_FLOW_STEERING_CAP_VLAN_PUSH_ON_RX
  MLX5_FLOW_STEERING_CAP_VLAN_POP_ON_TX

They map to DR_ACTION_STATE_PUSH_VLAN and DR_ACTION_STATE_POP_VLAN
actions, implemented in SW steering earlier in commit f5e22be5


("net/mlx5: DR, Split modify VLAN state to separate pop/push states").
Which enables using of pop/push vlan without restrictions, e.g. doing
vlan pop on TX and RX, compared to FW steering that supports only vlan
pop on RX and push on TX.

Other capabilities can be added in the future.

Signed-off-by: Dima Chumak <dchumak@nvidia.com>
Reviewed-by: Mark Bloch <mbloch@nvidia.com>
Reviewed-by: Yevgeny Kliteynik <kliteyn@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>