Yes that would be the error rate to the ONT. I'm not that familiar with PPPoE setups but I'd guess that you could also doSo the error rate is 0.07 %. I have no idea of what is "normal" in any case it's quite low IMHO.
ifconfig ppp0to get the stats for that link. (Or do
ifconfig -aand look at all the interfaces. )
But for your actual question about errors on the LAN connections; thinking about this a bit more I suspect that because br0 isn't a physical interface (it's a bridge) that it will never report any errors. At least I've never seen any. To find the actual interface name look at the output of
brctl show. I suspect it will be called vlan1. So you could then look for errors with
ifconfig vlan1. But again, it's a virtual interface not a physical one so I doubt it will report anything useful.
So I think the only way to detect errors would be to send traffic down the links and look for lost packets. There aren't really any good tools to do this built into the firmware. Does the RT-N16U have Entware installed? That would allow you to install some more useful tools.