mlxsw: spectrum: Add trap for multicast trap-and-forward routes

When a multicast route is configured with trap-and-forward action, the
packets should be marked with skb->offload_mr_fwd_mark, in order to prevent
the packets from being forwarded again by the kernel ipmr module.

Due to this, it is not possible to use the already existing multicast trap
(MLXSW_TRAP_ID_ACL1) as the packet should be marked differently. Add the
MLXSW_TRAP_ID_ACL2 which is for trap-and-forward multicast routes, and set
the offload_mr_fwd_mark skb field in its handler.

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