Properly detect changes to Netbox SNMP profiles

The ipdevpoll-internal Netbox data structure needs to be udpated when
the netbox' preferred SNMP profile has changed in the database, to
ensure we can still communicate with the netbox.

This is simply done by comparing the new computed `snmp_parameters`
attribute.  But, we must also remember to actually store the new value
in the Netbox.copy() method.

python/nav/ipdevpoll/dataloader.py

@@ -178,9 +178,9 @@ def is_netbox_changed(netbox1, netbox2):
         'type',
         'up',
         'snmp_up',
+        'snmp_parameters',
         'deleted_at',
     ):
-        # TODO Need some way to detect an updated SNMP profile
         if getattr(netbox1, attr) != getattr(netbox2, attr):
             _logger.debug(
                 "%s.%s changed from %r to %r",

python/nav/ipdevpoll/shadows/netbox.py

@@ -62,13 +62,15 @@ def is_up(self):
         return self.up == manage.Netbox.UP_UP
 
     def copy(self, other):
+        """In addition to copying the 'official' attrs of another Netbox object,
+        this also copies 'computed'/'internal' attributes that are only part of the
+        Netbox shadow class definition.
+        """
         super(Netbox, self).copy(other)
         for attr in (
             "snmp_up",
             "last_updated",
-            "snmp_version",
-            "read_only",
-            "read_write",
+            "snmp_parameters",
         ):
             if hasattr(other, attr):
                 setattr(self, attr, getattr(other, attr))