fix: change snr_pkt type from uint8_t to int8_t for correct SNR representation

inc/llcc68_definitions.hpp

@@ -407,7 +407,7 @@ struct __attribute__((packed)) lora_packet_status_t {
 	uint8_t rssi_pkt;
 	// Estimation of SNR on last packet received in two’s compliment format multiplied by 4.
 	// Actual SNR in dB =SnrPkt/4
-	uint8_t snr_pkt;
+	int8_t snr_pkt;
 	// Estimation of RSSI of the LoRa® signal (after despreading) on last packet received.
 	// Actual Rssi in dB = -SignalRssiPkt/2
 	uint8_t signal_rssi_pkt;