dns response handling: don't treat too many addresses as an error

dns response handling: don't treat too many addresses as an error

returning -1 rather than 0 from the parse function causes __dns_parse
to bail out and return an error. presently, name_from_dns does not
check the return value anyway, so this does not matter, but if it ever
started treating this as an error, lookups with large numbers of
addresses would break. this is a consequence of adding TCP support and
extending the buffer size used in name_from_dns.