rtcpbuffer: add support XR packet parsing
Imported from bugzilla
According to RFC3611, the extended report blocks in XR packet can have variable length. To visit each block, the iterator should look into block header. Once XR type is extracted, users can parse the detailed information by given functions.
Loss/Duplicate RLE The Loss RLE and the Duplicate RLE have same format so they can share parsers. For unit test, randomly generated pseudo packet is used.
Packet Receipt Times The packet receipt times report block has a list of receipt times which are in [begin_seq, end_seq).
Receiver Reference Time paser for XR packet The receiver reference time has ntptime which is 64 bit type.
DLRR The DLRR report block consists of sub-blocks which has ssrc, last RR, and delay since last RR. The number of sub-blocks should be calculated from block length.
Statistics Summary The Statistics Summary report block provides fixed length information.
VoIP Metrics VoIP Metrics consists of several metrics even though they are in a report block. Data retrieving functions are added per metrics.
Closes #395 (closed)