Fixed a race condition for IWLAN handover

Fixed a race that after handover data setup successfully,
telephony incorrectly informed connectivity service that
data is disconnected if the original data connection was
disconnected by itself before telephony had a chance to
disconnect it.

Fixed by adding a transport type once the network agent
is successfully transferred to the new data connection.

Test: Manual
Bug: 127495896
Change-Id: I0979580319fba15c28e7974e2ec31e6f48426840