mlxsw: Add layer 3 devlink-trap exceptions support

Add the trap IDs used to report layer 3 exceptions.

Trapped packets are first reported to devlink and then injected to the
kernel's receive path. All the packets have 'offload_fwd_mark' set in
order to prevent them from potentially being forwarded by the bridge
again.

Signed-off-by: Amit Cohen <amitc@mellanox.com>
Acked-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: Ido Schimmel <idosch@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>