config sepolicy to allow netd to write to statsd.

Test: run runtests.sh, make sure no missing test and get all pass
      run /out/host/linux-x86/bin/statsd_testdrive 82
      Got following metric data dump:pass for local test
Bug: 119862317

Change-Id: Ieff5ca55de46715d54ef57c4a6d144fd7d03e4b7