servicedvb: implement iStreamedService

eDVBServicePlay::streamed modifications:
When m_is_stream is false we keep old behaviour (ptr = 0; return -1;)
When m_is_stream is true we return valid pointer (ptr = this; return 0;)

After this change Converter ServiceInfo will display correct information on IsStream.

Also getBufferCharge and setBufferSize need to be implemented,
getBufferCharge currently returns dummy, setBufferSize returns success.