getTcpBytesReceived/getTcpBytesSent does not exist in API 19+. Fix with ...

The reflection of getTcpBytesReceived/getTcpBytesSent in BatteryStatsProxy.getNetworkUsageStats fails with API 19+. These two methods are [replaced with getNetworkActivityCount](http://grepcode.com/file/repo1.maven.org/maven2/org.robolectric/android-all/4.4_r1-robolectric-0/com/android/internal/os/BatteryStatsImpl.java/). The commit add a switch based on the API level.