mlxsw: core: Remove unused action field from mlxsw_rx_listener struct

Commit 0791051c ("mlxsw: core: Create a generic function to
register / unregister traps") moved this field to struct mlxsw_listener,
but forgot to remove it from struct mlxsw_rx_listener.
Remove the unused field.

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>