mlxsw: spectrum: Set LAG port collector only when active

The LAG port collecting (receive) function was mistakenly set when the
port was registered as a LAG member, while it should be set only when
the port collection state is set to true. Set LAG port to collecting
when it is set to distributing, as described in the IEEE link
aggregation standard coupled control mux machine state diagram.

Signed-off-by: Nir Dotan <nird@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>