Actually close sockets when stopping the receive thread.

Contrary to the expectations of the code, IoUtils.closeQuietly()
does not unblock system calls. So mReceiveThread.halt() was not
actually stopping the receive thread.

This wasn't actually a problem, because after "stopping" the
receive thread, either the interface would go down (interrupting
the previous receive thread with ENETDOWN), or a packet would
arrive to both the old and new receive threads, stopping the
old one. But the lack of a "stopping receive thread" message at
the expected time was confusing.

While I'm at it, also add the string for CMD_TIMEOUT.

Bug: 19704592
Change-Id: I74732429118af780453028898148519b294fa9d3