Fix python caching flags of old packets

twnet_parser/packet.py

@@ -43,7 +43,7 @@ class PacketFlags6(PrettyPrint):
 class PacketHeader(PrettyPrint):
     def __init__(
             self,
-            flags: PacketFlags7 = PacketFlags7(),
+            flags: Optional[PacketFlags7] = None,
             ack: int = 0,
             token: bytes = b'\xff\xff\xff\xff',
             num_chunks: Optional[int] = None
@@ -53,6 +53,8 @@ class PacketHeader(PrettyPrint):
         the messages it was given when
         the pack() method is called
         """
+        if not flags:
+            flags = PacketFlags7()
         self.flags: PacketFlags7 = flags
         self.ack: int = ack % NET_MAX_SEQUENCE
         self.token: bytes = token