Refactor some of the OSNetworkSystem stuff to more appropriate homes.

Also rewrite PlainDatagramSocketImpl.peek in terms of existing primitives
rather than requiring its own. I still don't see how it can get called, but
at least now it doesn't require its own native code.

Bug: 2686833

Change-Id: I0453add66dab4c7095ee2a3f51a49efbd1205598
13 files changed