network: reintroduce network.debug (#5093)

network.debug and interface.debug were removed during the asyncio-aiorpcx
network-rewrite.

electrum/network.py

@@ -276,6 +276,9 @@ class Network(PrintError):
         self.server_queue = None
         self.proxy = None
 
+        # Dump network messages (all interfaces).  Set at runtime from the console.
+        self.debug = False
+
         self._set_status('disconnected')
 
     def run_from_another_thread(self, coro):