Issue(#63) correct the maximum payload length in RX mode.
Issue(#63) correct the maximum payload length in RX mode.

imec-idlab/LoRaMac-node,imec-idlab/LoRaMac-node,seanelaval/LoRaMac-node,abouillot/LoRaMac-node,seanelaval/LoRaMac-node,abouillot/LoRaMac-node,seanelaval/LoRaMac-node,reixd/LoRaMac-node,reixd/LoRaMac-node