dnsmasq: tighten config file permissions

dnsmasq: tighten config file permissions

Install following as config files (600) perms instead of as data (644)

/usr/share/dnsmasq/dhcpbogushostname.conf
/usr/share/dnsmasq/trust-anchors.conf
/usr/share/dnsmasq/rfc6761.conf
/etc/hotplug.d/ntp/25-dnsmasqsec
/etc/config/dhcp
/etc/dnsmasq.conf

dnsmasq reads relevant config files before dropping root privilege and
running as dnsmasq:dnsmasq

ntpd runs as root so the hotplug script is still accessible

Signed-off-by: Kevin Darbyshire-Bryant <ldir@darbyshire-bryant.me.uk>
(backported from 3dba85254719215747e150301081477a47b38645)