samples: Bluetooth: Make broadcaster_multiple run on other controllers

`CONFIG_BT_CTLR_ADV_DATA_CHAIN` is a Zephyr Controller exclusive.
Use the max length instead to decide if we should add more data.

The motivation for the change is that tests/bsim/bluetooth/host/adv/chain
does not pass with Nordic's Softdevice Controller because of this.

Signed-off-by: Jonathan Rico <jonathan.rico@nordicsemi.no>