Refactored glances.plugins.ip.PluginModel.update

* part of #2801
* formatted into a dict; if input method is SNMP, returns default stats
* if input method is local, calls `get_stats_for_local_input`
* it has three steps:  `get_private_ipv4`, `get_first_ipv4`, `get_public_ipv4`.

Signed-off-by: Ariel Otilibili <otilibil@eurecom.fr>

glances/plugins/ip/__init__.py

@@ -95,6 +95,8 @@ def update(self):
         # Init new stats
         stats = self.get_init_value()
 
+        # Revert
+
         if self.input_method == 'local' and not import_error_tag:
             # Private IP address
             # Get the default gateway thanks to the netifaces lib