Update dns_spoof.c

Improved the logic around `parse_line()` and parsing of SRV records. The returned IP4/6-address is ambiguous for SRV records since it can AFAIK be either IPv4 or IPv6. `is_ip6` is set accordingly. Also check for lines with only newlines. `ip_tmp[]` need not be static in `parse_line()`. Lots of white-space changes.