ASACORE-776: Fix logic in TTL expiry on sender side

Update SND.UNA correctly when last unacked message expires.
Plus, fix condition for turning persist timer on/off.

Change-Id: Ib521d62994f154c5b3928a3a0317693a9c8c0390
Signed-off-by: Inga Stotland <ingas@qce.qualcomm.com>
Merge "ASACORE-776: Fix logic in TTL expiry on sender side" into feature/udp_transport
Merge remote-tracking branch 'origin/feature/udp_transport' into temp/integration-14.10

Change-Id: I6d644151ffc156b9f79b240b1a58e775cd2da97f
Signed-off-by: QCE Seabuild <qce.seabuild@qce.qualcomm.com>