mlxsw: Add trap group for control packets

Previously, we trapped flooded and control packets using the same trap
group. This can cause flooded packets to overflow the PCI bus and
prevent control packets (e.g. STP, LACP) from getting to the CPU.

Solve this by splitting the RX trap group to RX and control, which allows
us to configure a policer on the first, thereby preventing it from
overflowing the PCI bus.

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