[FS#559] No Ethernet statistics on ag71xx

[LEDE Bugs]

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FS#559 - No Ethernet statistics on ag71xx
User who did this: Yousong Zhou (yousong)
Reported Version: lede-17.01 -> Trunk

More information can be found at the following URL:
https://bugs.lede-project.org/index.php?do=details&task_id=559