LibAAH_RTP: Properly handle EOS conditions.

EOS was being treated as a flush operation which was causing problems.
In particular, the transmitter was delcaring that playback was
complete early (by the clock lead time of the system, which was 1
second in this case).  Also, the receiver was treating the EOS message
just like the flush message, immediately destroying the substreams
associated with the program without letting them play out first.

Change the transmitter to send the EOS message like it always does,
but have it wait until the media time of the last sample has arrived
before reporting playback complete to the app level of things.

On the receiver side of things, don't treat the EOS message like the
flush message.  Instead, have the EOS message simply put the substream
into EOS mode, allowing it to signal EOS to its decoder and shut off
the isAboutToUnderflow hack.

Change-Id: Ibe3ac01044373f83edb7a5f4b70478bd78c16d11