network: fix switching interface (restart old one)

follow-up b3ff173b45
connection_down was killing the already restarted old interface

electrum/interface.py

@@ -253,7 +253,7 @@ class Interface(PrintError):
             except GracefulDisconnect as e:
                 self.print_error("disconnecting gracefully. {}".format(e))
             finally:
-                await self.network.connection_down(self.server)
+                await self.network.connection_down(self)
                 self.got_disconnected.set_result(1)
         return wrapper_func
 

electrum/network.py

@@ -638,14 +638,14 @@ class Network(PrintError):
         self.recent_servers = self.recent_servers[0:20]
         self._save_recent_servers()
 
-    async def connection_down(self, server):
+    async def connection_down(self, interface: Interface):
         '''A connection to server either went down, or was never made.
         We distinguish by whether it is in self.interfaces.'''
+        if not interface: return
+        server = interface.server
         self.disconnected_servers.add(server)
         if server == self.default_server:
             self._set_status('disconnected')
-        interface = self.interfaces.get(server, None)
-        if interface:
         await self._close_interface(interface)
         self.trigger_callback('network_updated')