[KA03] Support tcp keepalive offload

When offload is starting, socket will be switched to repair
mode. Read and write on the socket will not be allowed until
repair mode is turned off. If remote packet arrives, repair
mode will be turned off automatically and a callback will
be raised to indicate that socket is ready to read from.

Bug: 114151147
Test: -atest FrameworksNetTests
      -manual

Change-Id: I0c335865912e183e7ad32a8ea12188f02ccde5fd