Debian: Write pid-file in the correct place when using systemd.

debian/init

@@ -279,6 +279,7 @@ case "$1" in
   systemd-exec)
 # Enable DBus by default because we use DBus activation with systemd.
 	exec $DAEMON --keep-in-foreground --enable-dbus \
+	    -x /var/run/dnsmasq/$NAME.pid \
 	    ${MAILHOSTNAME:+ -m $MAILHOSTNAME} \
 	    ${MAILTARGET:+ -t $MAILTARGET} \
 	    ${DNSMASQ_USER:+ -u $DNSMASQ_USER} \