Fix deferred netvm feature name

Author: ben-grande

qubes/vm/mix/net.py

@@ -454,7 +454,7 @@ def detach_network(self):
 
         if not self.is_running():
             raise qubes.exc.QubesVMNotRunningError(self)
-        deferred_from = self.features.get("deferred-netvm", None)
+        deferred_from = self.features.get("deferred-netvm-original", None)
         if self.netvm is None:
             if deferred_from is not None:
                 raise qubes.exc.QubesVMError(