Start SecurityLogMonitor after broadcasts are allowed.

Otherwise if boot takes long enough, DO broadcast will be sent while
ActivityManagerSerivce is not ready, causing IllegalStateException.

Change-Id: I6b55ed45ed7b1f3ed9ad6ec20695907b4fa6f3b1
Fixes: 109746888
Test: atest CtsDevicePolicyManagerTestCases:com.android.cts.devicepolicy.DeviceOwnerTest#testSecurityLoggingWithSingleUser
Test: provisioned TestDPC as DO in SuW, enabled logging.