Upgrade dns/dnsmasq to v2.80.

Security: the installed example configuration file shows a way of
disabling WPAD hijacking, but leaves it commented out. Extend pkg-message.

Changelog: http://thekelleys.org.uk/dnsmasq/CHANGELOG

Since installing v2.80 isn't a fix against the vulnerability, and fixing
it needs administrator intervention on upgrades, I am not marking this in
vuxml for now, since we'd need to mark v2.80 vulnerable, too.

MFH: 2018Q4
Security: CERT VU#598349