session: basic fifo-tuning-logic

session: basic fifo-tuning-logic

- Allowing application to register custom fifo-tuning-logic.
- Adding an example custom fifo-tuning-logic in hs_app/proxy.

Type: feature

Signed-off-by: Ryujiro Shibuya <ryujiro.shibuya@owmobility.com>
Signed-off-by: Florin Coras <fcoras@cisco.com>
Change-Id: I2aca14d1f23d5c3c9debb7f4c46aca3a15a8d1b9