Nicolas Dufresne authored May 07, 2019 and Nicolas Dufresne committed May 21, 2019

As we can now have multiple sessions, stats need to be implemented per
session. This follow RTPSession model with sources. The stats are now:

    dropped: 0
    received: 0
    recovered: 0
    permanently-lost: 0
    duplicates: 0
    retransmission-requests-sent: 0
    rtx-roundtrip-time: 0
    session-stats:
        session-id=0
            rtp-from=""
            rtcp-from=""
            dropped=0
            received=0
        session-id=1
            rtp-from=""
            rtcp-from=""
            dropped=0
            received=0
        . . .

session-stats is a GValueArray as there is no better alternatives.