Close statsd log socket before zygote fork().

MetricsLogger will start to write to statsd instead of logd. Zygote uses
MetricsLogger too. So we need to close statsd socket before zygote fork() is
called (see b/30963384 for context).

Bug: 110537511
Test: Manually verified that it successfully boots with no crash with
ag/5112579 and ag/5169664 (together)

Change-Id: Id550fbd5ac2f6ca47d3293c12fb537fafa3f33a0