Bugfix: plugin_geoip v4_overlay databases not reloading correctly

One of the timer callbacks involved in reloading the v4_overlay
databases was stopping the wrong timer, and the net result of that
was the update is never applied and the event keeps firing every
5 seconds over and over, issuing a syslog message like this
every time:

plugin_geoip: map 'x': Processing GeoIP database '/x/GeoIP.dat'
plugin_geoip: map 'x': Processing GeoIP database '/x/GeoIP.dat'
plugin_geoip: map 'x': Processing GeoIP database '/x/GeoIP.dat'
...