libstagefright: HTTP Streaming fixes

- Stop fetching on reaching EOS
- Disconnect datasource in player's reset
- Send buffering complete when seek is issued
  when player is in buffering state

Change-Id: If1650f02ffda10e0d8ca4a9c7fd0a5681d05e75e
Signed-off-by: jmeng <jmeng@codeaurora.org>