fix possible error caused by wrong datatype

src/shellmatta_transport.h

@@ -96,7 +96,7 @@ typedef struct
 
 extern uint8_t protocolVersion;
 extern shellmatta_transport_packet_t packetType;
-extern uint8_t payloadLength;
+extern uint32_t payloadLength;
 extern uint8_t source;
 extern uint8_t destination;
 extern uint32_t crc32;