core: fix handling uses_default_netvm property

- for netvm it doesn't make sense, but instead of removing it (which
        surely will break some code), make it always False
- when settings VM connections, uses_default_netvm is already loaded
- handle it properly during backup restore (really use default netvm,
        istead of assuming it's the same as during backup)

core-modules/005QubesNetVm.py

@@ -42,6 +42,7 @@ class QubesNetVm(QubesVm):
         attrs_config['dir_path']['func'] = \
             lambda value: value if value is not None else \
                 os.path.join(system_path["qubes_servicevms_dir"], self.name)
+        attrs_config['uses_default_netvm']['func'] = lambda x: False
         attrs_config['label']['default'] = defaults["servicevm_label"]
         attrs_config['memory']['default'] = 300
 

core/backup.py

@@ -1706,7 +1706,11 @@ def restore_info_verify(restore_info, host_collection):
 
         # check netvm
         vm_info.pop('missing-netvm', None)
-        if vm_info['netvm']:
+        if vm_info['vm'].uses_default_netvm:
+            default_netvm = host_collection.get_default_netvm()
+            vm_info['netvm'] = default_netvm.name if \
+                default_netvm else None
+        elif vm_info['netvm']:
             netvm_name = vm_info['netvm']
 
             netvm_on_host = host_collection.get_vm_by_name(netvm_name)

core/qubes.py

@@ -713,18 +713,13 @@ class QubesVmCollection(dict):
 
     def set_netvm_dependency(self, element):
         kwargs = {}
-        attr_list = ("qid", "uses_default_netvm", "netvm_qid")
+        attr_list = ("qid", "netvm_qid")
 
         for attribute in attr_list:
             kwargs[attribute] = element.get(attribute)
 
         vm = self[int(kwargs["qid"])]
 
-        if "uses_default_netvm" not in kwargs:
-            vm.uses_default_netvm = True
-        else:
-            vm.uses_default_netvm = (
-                    True if kwargs["uses_default_netvm"] == "True" else False)
         if vm.uses_default_netvm is True:
             if vm.is_proxyvm():
                 netvm = self.get_default_fw_netvm()