Fixed incorrect rssi calculation

Similar to pr riverloopsec#278 but these values work better

Author: Mageh533

killerbee/dev_cc253x.py

@@ -241,6 +241,12 @@ def pnext(self, timeout=100):
                 # in last two bytes of framedata. Note that we remove these before return of the frame.
 
                 # RSSI is signed value, offset by 73 (see CC2530 data sheet for offset)
+                # Possible fix for incorrect rssi calculation
+                rssi = struct.unpack('b', framedata[-2:-1])[0] - 73
+                if rssi > 127 or rssi < -128:
+                    print(f"Rssi = {rssi}, out of range, setting to 127")
+                    rssi = 127
+
                 rssi = framedata[-2] - 73
                 # Dirty hack to compensate for possible RSSI overflow
                 if rssi > 255: