libstagefright: extend the interface to switch rtp transport

- rtp transport can be changed by setting property "rtsp.
  transport.TCP" and udp is the first choice as
  default. But the property is the global variable and
  affects each instance's behaviour.
  Extend the interface of MyHandler to let each client make
  its own choice. If the client wants to choose tcp first,
  add the string/value "rtp.transport.TCP"/"true" in the headers
  when calling MediaPlayer.setDataSource.

Change-Id: I19b6192da36d5c00e62c9f69de446f366f10c75c
Crs-Fixed: 696569