peer linklocal address can't be negotiated in ipoe mode unlike ppp,
so route may lead to nowhere with non-working PD routing as result.
so, instead of guessing peer link-local address, use dhcpv6 client
src address as the gateway.
since dhcpv6 clients are onlink and there's no dhcpv6 relay support
(yet), dhcpv6 source would be exactly final linklocal address, no
matter ppp or ipoe is in use.
fine tune commit abaa43a307fa7a790dd34034c5fd8013dbd0488c
peer linklocal address can't be negotiated in ipoe mode unlike ppp, so route may lead to nowhere with non-working PD routing as result. so, instead of guessing peer link-local address, use dhcpv6 client src address as the gateway. since dhcpv6 clients are onlink and there's no dhcpv6 relay support (yet), dhcpv6 source would be exactly final linklocal address, no matter ppp or ipoe is in use.
fine tune commit abaa43a307fa7a790dd34034c5fd8013dbd0488c