[FS#1393] netifd: "ubus call network reload" can't remove the deprecated ipv6 prefix delegation on lan

[LEDE Bugs]

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FS#1393 - netifd: "ubus call network reload" can't remove the deprecated ipv6 prefix delegation on lan
User who did this - Kai Song (alfred.song)

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netifd maintains a state machine for each interface.
>From what I've found, "ubus call network reload" will not tear down all interfaces first, no change was applied to lan section in my test. Thus lan interface's state will still be UP after reload, it will not trigger the process in func interface_set_up() to remove/add the ip address of linux interface.
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More information can be found at the following URL:
https://bugs.openwrt.org/index.php?do=details&task_id=1393#comment4402