Adopt prev preferred APN on APN reset

To have the APN selected UI in sync with the currently connected network, while carrier config didn't specify any default APN, we adopt the previously preferred APN(the one used by the current connected network) if it's provided by carriers versus user created.

Fix: 237904428
Test: atest DataProfileManagerTest.java + manual
Change-Id: I27a9b62860a966ecfd84fc83ba70203136622ed0