L2SS-244: explicitly expose payload_error, as it is an important field.

devices/clients/SDP_statistics.py

@@ -109,6 +109,10 @@ class StatisticsPacket(object):
           "gn_index": get_bit_value(bits, 0, 4),
         }
 
+    @property
+    def payload_error(self) -> bool:
+        return self.source_info["payload_error"] == 1
+
     @property
     def reserved(self) -> bytes:
         """ Reserved bytes. """