Rename on_domain_shutdown to avoid DispVM clobbering the function

DispVM.on_domain_shutdown clobbers NetVMMixin.on_domain_shutdown. Rename
the latter to avoid that.

Author: marmarek

qubes/vm/mix/net.py

@@ -306,7 +306,7 @@ def on_domain_load_netvm_loop_check(self, event):
             self.netvm = None
 
     @qubes.events.handler("domain-shutdown")
-    def on_domain_shutdown(self, event, **kwargs):
+    def on_domain_shutdown_net(self, event, **kwargs):
         """Cleanup network interfaces of connected, running VMs.
 
         This will allow re-reconnecting them cleanly later.