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

[LEDE Bugs]

The following task has a new comment added:

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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It looks like something are missing in netifd to clear the deprecated ipv6 address of linux protocol stack.
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More information can be found at the following URL:
https://bugs.openwrt.org/index.php?do=details&task_id=1393#comment4393