ASACORE-938: adjust RTT calculation based on segment size

Also, rest RTT calculation when probe timer is fired and
no retransmits are present.

Change-Id: I6cdbbc3e43e140cc8bbd00641d00a55bee1083af
Signed-off-by: Inga Stotland <ingas@qce.qualcomm.com>
Merge "ASACORE-938: adjust RTT calculation based on segment size" into feature/udp_transport