Make EnabledNetworkModePreferenceController listen to setting changes

The controller for the "Preferred network type" preference on the SIM
details page wasn't listening for changes to the underlying global
setting, so changes to the setting would be reflected in SysUI but not
on this page if it happened to be showing.

Bug: 135667565
Test: make RunSettingsRoboTests
Change-Id: I5dfe4843a681c613f49caf4584e9dbebc54e708a
Merged-In: I5dfe4843a681c613f49caf4584e9dbebc54e708a