Fixed a race condition when preferred transport updated

This bug is only applicable on the old data stack on T.
Transport manager and access network manager might be running
on a different thread. Fixed a race condition on old data stack
that was introduced in early new data stack development time frame.
The transport evaluation could happen earlier than setting the
preferred transport due to the race condition.

Fixed by setting the preferred transport earlier than notifying
transport manager.

Fix: 226677098
Test: Sanity tests && atest FrameworksTelephonyTests
Merged-In: Id856902c9a73942913e041dc5396b5d17b661089
Change-Id: Id856902c9a73942913e041dc5396b5d17b661089