Last part of hop-limit determination is always:
    hoplimit = dst_metric(dst, RTAX_HOPLIMIT);
    if (hoplimit < 0)
        hoplimit = ipv6_get_hoplimit(dst->dev).

Let's consolidate it as ip6_dst_hoplimit(dst).
Signed-off-by: NYOSHIFUJI Hideaki <yoshfuji@linux-ipv6.org>