net/ipv6: Remove extra call to ip6_convert_metrics for multipath case

The change to move metrics from the dst to rt6_info moved the call
to ip6_convert_metrics from ip6_route_add to ip6_route_info_create. In
doing so it makes the call in ip6_route_info_append redundant and
actually leaks the metrics installed as part of the ip6_route_info_create.
Remove the now unnecessary call.

Fixes: d4ead6b3 ("net/ipv6: move metrics from dst to rt6_info")
Signed-off-by: David Ahern <dsahern@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>