Debian fix: Enable dnsmasq systemd unit on install.

debian/postinst

@@ -1,6 +1,22 @@
 #!/bin/sh
 set -e
 
+# Code copied from dh_systemd_enable ----------------------
+# This will only remove masks created by d-s-h on package removal.
+deb-systemd-helper unmask dnsmasq.service >/dev/null || true
+
+# was-enabled defaults to true, so new installations run enable.
+if deb-systemd-helper --quiet was-enabled dnsmasq.service; then
+	# Enables the unit on first installation, creates new
+	# symlinks on upgrades if the unit file has changed.
+	deb-systemd-helper enable dnsmasq.service >/dev/null || true
+else
+	# Update the statefile to add new symlinks (if any), which need to be
+	# cleaned up on purge. Also remove old symlinks.
+	deb-systemd-helper update-state dnsmasq.service >/dev/null || true
+fi
+# End code copied from dh_systemd_enable ------------------
+
 if [ -x /etc/init.d/dnsmasq ]; then
    update-rc.d dnsmasq defaults 15 85 >/dev/null