Switch to using android.system.Os for more calls

The methods being switched here should involve no important
semantic changes. socket.getSoTimeout() is now implemented:
previously it would have returned 0 in all cases.

Some tidy up of unimplemented / commented code.

Switching other calls to use Os would carry more risk and
will be handled separately they can be switched safely.

Bug: 3106438
Change-Id: I5526249395565fee6e43f159a2b5975b0d41d058