ipv6: Pass fib6_result to pcpu route functions

Update ip6_rt_pcpu_alloc, rt6_get_pcpu_route and rt6_make_pcpu_route
to a fib6_result over a fib6_info.

Signed-off-by: David Ahern <dsahern@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>