VT: adding RR(Reception Report) logic

[Problem] There is no way to measure RTT(Round Trip Time)
  in application layer.

[Cause] There is no interface defined to let application
  know the RR received.

[Solution] Define an interface for RR and report it
  to application.

Bug: 201473503
Test: Manually MMQoE test

Signed-off-by: Byeongjo Park <bjo.park@samsung.com>
Change-Id: Ia07d0a8996061dd26088c14a17c9f6776ae8e86d