USN-6657-2: Dnsmasq vulnerabilities

USN-6657-1 fixed several vulnerabilities in Dnsmasq. This update provides the corresponding update for Ubuntu 16.04 LTS and Ubuntu 18.04 LTS. Original advisory details: Elias Heftrig, Haya Schulmann, Niklas Vogel, and Michael Waidner discovered that Dnsmasq icorrectly handled validating DNSSEC...