It doesn't make any sense to allow policy routing (see ip-rule(8)) on
IPv4 but not on IPv6. If v6 is going to be there at all, it should have
the same features as v4. Also, multiple routing tables and policy
routing is just one of those standard Linux networking features people
expect to exist. Tutorials are peppered with its usage. Judging by the
inconsistent nature of its current enablement across different kernel
configs, I think it was just forgotten by accident from these configs.
So, this patch simply enables it again.
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>