Pivot network statistics to use DataInput/Output.

The majority of this refactoring has already landed in AOSP, and this
small CL is the remaining piece needed to begin using the new
optimized classes which only exist in the internal tree.

This is a no-op refactoring.

Bug: 176777285
Test: atest FrameworksNetTests CtsNetTestCases
Change-Id: Ifd7ac95c6cd6761e7d03cbf381dcc9e32b6406aa