mlxsw: spectrum_acl: Offload FLOW_ACTION_SAMPLE

Implement support for action sample when used with a flower classifier
by implementing the required sampler_add() / sampler_del() callbacks and
registering an Rx listener for the sampled packets.

The sampler_add() callback returns an error for Spectrum-1 as the
functionality is not supported. In Spectrum-{2,3} the callback creates a
mirroring agent towards the CPU. The agent's identifier is used by the
policy engine code to mirror towards the CPU with probability.

The Rx listener for the sampled packet is registered with the 'policy
engine' mirroring reason and passes trapped packets to the psample
module after looking up their parameters (e.g., sampling group).

Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Reviewed-by: Jiri Pirko <jiri@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>