mcq-ipv6: traceroute: comment for positive answers

These traceroute's are correct but note that it's likely possible that the penultimate address will be an other IPv6 address of the same router: it depends if the ICMP package takes the path to the previous router or to the source (the reversed path is different according to the forwarding tables).
Merge pull request #114 from matttbe/patch-2

mcq-ipv6: traceroute: comment for positive answers