Whenever the network module is configured with both "format" and
"format-$state" and when the module use "format-$state" once, it
override the value that was saved from "format".
For example, if both "format" and "format-disconnect" are configured,
and only those, as soon as the module show information about a
disconnected interface, it will keep showing the format for
disconnected, even if the interface is connected again later.
Fix that by always setting a value to default_format_ in update() and
thus use the intended default format when needed.
Fixes#1129
194f4c2f18