misc: replaced all "dummy" by the more conventional and readable "__" ("_" being used for gettext)

sat/plugins/plugin_misc_nat-port.py

@@ -105,7 +105,7 @@ class NatPort(object):
         @return (None, str): found IP address, or None of something got wrong
         """
 
-        def getIP(dummy):
+        def getIP(__):
             if self._upnp is None:
                 return None
             # lanaddr can be the empty string if not found,