Change BlockingSocketReader to use MessageQueue fd handling

Convert the simplistic blocking read in a separate thread model to
the MessageQueue OnFileDescriptorEventListener model, albeit still
on a separate thread.

Test: as follows
    - built
    - flashed
    - booted
    - "runtest frameworks-net" passes
    - basic IpManager functions still work,
      including ConnectivityPacketTracker
Bug: 62476366
Bug: 67013397
Change-Id: I1f4a6707eba402338947fe3f5392a26660f05714