Implement packet loss calculations in Receiver Reports

In order to support servers that have implemented the
dynamic bandwidth adaptation feature are these
fields added to the receiver report:
      -Fraction
      -Cumulative number of packet loss

The calculation is based on RFC 3550, section A.3.

Test: play RTSP video and check receiver reports with network tool
Bug: 62610498

Change-Id: I2092fb62698e7209c59fade1b17a6460ac236def