mlxsw: spectrum_span: Allow setting policer on a SPAN agent

When mirroring packets to the CPU port the mirrored packets are trapped
to the CPU. However, unlike other traps, it is not possible to set a
policer on the associated trap group. Instead, the policer needs to be
set on the SPAN agent.

Moreover, the policer ID must be within a specified range: From a
configurable (even) base ID to this base plus the maximum number of SPAN
agents.

While the immediate use case is to set the policer on a SPAN agent that
mirrors to the CPU port, a policer can be set on any SPAN agent.
Therefore, the operation is implemented for all SPAN agent types.

Extend the SPAN agent request API to allow passing the desired policer
ID that should be bound to the SPAN agent. Return an error for
Spectrum-1, as it does not support policer setting on a SPAN agent.

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