[FS#57] brcm47xx-legacy target not always catching changes to files overlay

[LEDE Bugs]

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FS#57 - brcm47xx-legacy target not always catching changes to files overlay
User who did this: Felix Fietkau (nbd)
Status: Requires testing -> Waiting on reporter

More information can be found at the following URL:
https://bugs.lede-project.org/index.php?do=details&task_id=57