- Refine how DFS is calulated now that it is strictely used to
manipulate buffer lengths.
- Fix threshold limit
- Tune RX threshold relevantly (reduce it if rx_len is lower than actual)
- Don't push more than available left space in FIFO
- Tune the private structure to lower memory space occupation
Change-Id: I65b1b48b996b2104cebcb24cc366fb4dcbf7d53b
Signed-off-by: Tomasz Bursztyka <tomasz.bursztyka@linux.intel.com>