mlxsw: core: Allow to enable/disable rx_listener for trap

For source traps, the "thin policer" is going to be used in order
to reduce the amount of trapped packets to minimum. However, there
will be still small number of packets coming in that need to be dropped
in the driver. Allow to enable/disable rx_listener related to specific
trap in order to prevent unwanted packets to go up the stack.

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