[Status Bar] Allow carrier merged to be displayed even in airplane mode.

Fixes: 291993542
Test: manual: be in airplane mode, then trigger carrier merged via demo
mode (adb shell am broadcast -a com.android.systemui.demo -e command
network -e wifi carriermerged -e level 4 -e slot 4) -> verify triangle
with W+ displays
Test: atest FullMobileConnectionRepositoryTest MobileIconInteractorTest
MobileIconViewModelTest

Change-Id: Ie9ca23724891ae6563557bc2c82980723b2e5015