dns/dnsmasq: cherry-pick several upstream fixes

all from dnsmasq's Git repository hosted by Simon Kelley:

+ Fix DHCPv6 "use multicast" response
+ Avoid undefined behaviour with the ctype(3) functions.
+ Document suppressing default options in --dhcp-option.
+ Fix --rev-server option.
+ Set the default maximum DNS UDP packet size to 1232.
+ Generalise cached NXDOMAIN replies.
+ Fix possible SEGV when no servers defined.

and bump PORTREVISION. This is so we can let it mature
for two weeks before 2023Q2 and because the upstream
release schedule is unforeseeable.

Obtained from: Simon Kelley <simon@thekelleys.org.uk>
Obtained from: Dominik Derigs <dl6er@dl6er.de>
Obtained from: Taylor R Campbell <campbell+dnsmasq@mumble.net>