[Wi-Fi] Fix multi SIM devices switch to mobile data automatically settings missing problem

Context#getResources loading is done based on the last SIM to
come up, we may get wrong customization settings.

This fix check all active subscriptions and shows the preference
when there is one SIM applies.

Bug: 138956509
Test: CellularFallbackPreferenceControllerTest
      manual test:
          1. Insert feature supported SIM and check UI.
          2. Remove feature supported SIM and check UI.
          3. Turn airplane mode on and check 1. and 2..

Change-Id: I72b6db415429181395a02f163889bb1b9c0f070f