Add getMaxAllowedDataMode() on SatelliteController

Bug: 415427102
Test: 1. atest frameworks/opt/telephony/tests/telephonytests/src/com/android/internal/telephony/satellite/SatelliteControllerTest.java
2. Manual test:
Cap maxAllowedDataMode device config to 2 (SATELLITE_DATA_SUPPORT_ALL)
for test purpose. Then use Phone Info test UI to toggle between
restricted, constrained and unlimited data modes, to verify that:
2.1 data doesn't work inrestricted mode
2.2 data works only in apps with constrained setting in constrained mode
2.3 data works in any app in unlimited mode
Also, verified by QA - b/416599833#comment3

Flag: EXEMPT bug fix
Change-Id: Id442ffd3c9394f6eee4d891bdcc75b81648ceea6