Reworked assignment of FRSH contract parameters

Reworked assignment of FRSH contract parameters

Now we can specify also deadline. The assigned values differ for RTCP and
RTP streams because RCP needs much less bandwidth.

Sending was changed to sync. When async was used, the packets would
be queued and delivered with delay, which is not what we want. In future,
we might add an endpoint parameter to specify the size of queue and use
async again.