inet: allow scope in `uv_inet_ntop` ip6 check

see https://github.com/joyent/node/issues/7395

@saghul, basically we already support link local interface name/scope in `uv_ip6_addr`, but `uv_inet_ntop` does not recognize it. With this patch - it will not fail on encountering it.

There are two questions about it:

* Is it a new feature or a bug fix? (I think the latter one)
* Should it fail if `UV_PLATFORM_HAS_IP6_LINK_LOCAL_ADDRESS` is not present

@tjfontaine: are you fine with this in node v0.10 ?