ipv6: Pass fib6_result to rt6_device_match

Pass fib6_result to rt6_device_match with f6i set. rt6_device_match
updates f6i in the result if it finds a better match and sets nh.

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