Added support for QoS Level −1 (tested against RSMB)
Added support for QoS Level −1 (tested against RSMB)

MichalFoksa/mqtt-sn-tools,adamrenner/mqtt-sn-tools-contiki,MichalFoksa/mqtt-sn-tools,njh/mqtt-sn-tools,adamrenner/mqtt-sn-tools-contiki,njh/mqtt-sn-tools,adamrenner/mqtt-sn-tools-contiki