Reject packets with source of 0.0 from extended networks.

Packets from extended networks must have a source network specified. Anything coming from node `0.0` is clearly invalid and should be discarded. Note that the Linux 6.9 and newer include a revised AppleTalk kernel module that sometimes outputs packets with a source of `0.0`, which was causing TashRouter to crash. Fixes #8

Author: NJRoadfan

tashrouter/router/router.py

@@ -71,6 +71,9 @@ def stop(self):
 
   def inbound(self, datagram, rx_port):
     '''Called by a Port when a Datagram comes in from that port.  The Datagram may be routed, delivered, both, or neither.'''
+    # if we receive a packet from source node 0.0 on an extended network, discard it
+    if datagram.source_network == 0x0000 and datagram.source_node == 0x00 and rx_port.extended_network == True:
+      return
 
     # a network number of zero means "this network", but we know what that is from the port, so sub it in
     # note that short-header Datagrams always have a network number of zero