Security fix, CVE-2017-14496, Integer underflow in  DNS response creation.
    
        Fix DoS in DNS. Invalid boundary checks in the
        add_pseudoheader function allows a memcpy call with negative
        size An attacker which can send malicious DNS queries
        to dnsmasq can trigger a DoS remotely.
        dnsmasq is vulnerable only if one of the following option is
        specified: --add-mac, --add-cpe-id or --add-subnet.
    
    Signed-off-by: Petr Menšík <pemensik@redhat.com>