BUG/MINOR: dns: allow 63 char in hostname

BUG/MINOR: dns: allow 63 char in hostname

hostname were limited to 62 char, which is not RFC1035 compliant;
- the parsing loop should stop when above max label char
- fix len label test where d[i] was wrongly used
- simplify the whole function to avoid using two extra char* variable

this should fix github issue #387

Signed-off-by: William Dauchy <w.dauchy@criteo.com>
Reviewed-by: Tim Duesterhus <tim@bastelstu.be>
Acked-by: Baptiste <bedis9@gmail.com>