Store the preferred network mode only if it set to modem successfully

In Q, the phoneInterfaceManager store the preferred network type when it
set to modem successfully. Keep the behavior same as before.

Bug: 160201328
Test: Atest and by manual
Change-Id: Ieb0f48bf849ce5c9a9b3b8d4192a755a6f0adb3a
1 file changed