network: document and add type hint for NetworkDev.info

Signed-off-by: Olivier Gayot <olivier.gayot@canonical.com>

subiquitycore/models/network.py

@@ -21,6 +21,7 @@ from socket import AF_INET, AF_INET6
 from typing import Dict, List, Optional
 
 import attr
+import probert.network
 import yaml
 
 from subiquitycore import netplan
@@ -189,13 +190,16 @@ class BondParameters:
     ]
 
 
-class NetworkDev(object):
+class NetworkDev:
     def __init__(self, model, name, typ):
         self._model = model
         self._name = name
         self.type = typ
         self.config = {}
-        self.info = None
+        # Devices that have been configured in Subiquity but do not (yet) exist
+        # on the system have their "info" field set to None. Once they exist,
+        # probert should pass on the information through a call to new_link().
+        self.info: Optional[probert.network.Link] = None
         self.disabled_reason = None
         self.dhcp_events = {}
         self._dhcp_state = {