Fix SntpClient 2036 issue (1/2) am: f663ab42 am: 87fe4ba6 am: 741fb2db am: 970c0367

core/java/android/net/SntpClient.java

core/java/android/net/sntp/Duration64.java

core/java/android/net/sntp/Timestamp64.java

core/tests/coretests/src/android/net/SntpClientTest.java

.../tests/coretests/src/android/net/sntp/Duration64Test.java

...tests/coretests/src/android/net/sntp/Timestamp64Test.java