mlxsw: cmd: Add CONFIG_PROFILE.{set_, }lag_mode

Add CONFIG_PROFILE.lag_mode, which serves for moving responsibility for
placement of the LAG table from FW to SW. Whether lag_mode should be
configured is determined by CONFIG_PROFILE.set_lag_mode, which also add.

Signed-off-by: Petr Machata <petrm@nvidia.com>
Reviewed-by: Ido Schimmel <idosch@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>