pppoe0 keeps saying "nd6_na_input: duplicate IP6 address"

Kia ora,
I've been getting this message on my router console since forever and I 
think I've tracked down where it's coming from.

I use dhcpcd on my router to fetch IPv4 and IPv6 addresses from my ISP. 
 From time to time an NA packet is sent out my pppoe0 link to tell the 
other end that yes indeed, I am still here.

This NA packet is fed back up my routers own IPv6 stack to 
nd6_na_input() which has a specific check to ignore its own NA packets 
being sent out. This check is done by comparing link layer addresses on 
the packet and all available interfaces.

This doesn't work because pppoe interfaces (and packets on them) don't 
have link layer addresses to compare.

At least, I think that's what's going on.

Is there some way to make the IPv6 stack a little bit smarter so 
outgoing NA packets don't get fed back into nd6_na_input()?

I guess I could also look at an option so that dhcpcd doesn't send these 
packets on PPPoE links, but I don't actually have a problem with my 
router reminding my ISP that I really am still here from time to time.

Ngā-mihi,
Lloyd