[FS#742] LuCI csrf token error after upgrading from OpenWRT 15.05.1 to LEDE 17.01.1

[LEDE Bugs]

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FS#742 - LuCI csrf token error after upgrading from OpenWRT 15.05.1 to LEDE 17.01.1
User who did this: Yousong Zhou (yousong)
Summary: Cannot "upgrade" from OpenWRT 15.05.1 to LEDE 17.01.1 -> LuCI csrf token error after upgrading from OpenWRT 15.05.1 to LEDE 17.01.1

More information can be found at the following URL:
https://bugs.lede-project.org/index.php?do=details&task_id=742