[FS#1141] Don't show WAN status on Luci Overview page if there are no WAN interfaces

[LEDE Bugs]

The following task has a new comment added:

FS#1141 - Don't show WAN status on Luci Overview page if there are no WAN interfaces
User who did this - Jo-Philipp Wich (jow-)

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LuCI displays the interface carrying the default route as WAN.
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More information can be found at the following URL:
https://bugs.lede-project.org/index.php?do=details&task_id=1141#comment3765