access/srt: cleanup

1. srt: obsolete SRT_PARAM_CHUNK_SIZE and SRT_PARAM_PAYLOAD_SIZE

   Firstly, SRTO_PAYLOADSIZE has no effect for receiver. Secondly, since there is no negotiation of payload size between sender and receiver, the receiver should use a buffer at least SRT_LIVE_MAX_PLSIZE bytes, otherwise the data can be truncated. So the default value of option SRT_PARAM_CHUNK_SIZE is inappropriate. User may know exactly the sender's payload size to set the value for SRT_PARAM_CHUNK_SIZE, but there is no much gain for doing that.

2. srt: Fix missing srt_cleanup on error path

3. srt: initialize p_sys->sock to SRT_INVALID_SOCK

   Otherwise the zero initialized p_sys->sock will be closed in srt_schedule_reconnect().

4. srt: comment out too verbose log