[Mobile] Make sure we +1 the reported level if INFLATE_SIGNAL_STRENGTH is true

The carrier config key INFLATE_SIGNAL_STRENGTH instructs SystemUI to
create a 5-level mobile icon, as well as instructs us to add 1 to the
level reported from telephony. This change ensure that that is
happening.

Test: MobileConnectionRepositoryTest
Test: MobileIconInteractorTest
Fixes: 328547883
Flag: NONE
Change-Id: Iec6e8803cd84e646107b363e84c7331a81902945