statsd.go: fix UDP connection leak.
statsd.go: fix UDP connection leak.

GOP reconnects the statsd client every minute by default, and it doesn't
close the client before connecting again. I observed on a device a lot
of UDP sockets with random ports appearing / disappearing. I expect they
just time-out, but it's probably a good idea to explicitly close them
here as well.

The random port comes from how statsd sets it's connection up, it uses
the ":0" UDP address syntax for the net. lib to pick an available port.

cocoonlife/gop