Update BITMASK_2G to include 1xRTT when disabling/enabling 2G
via toggle in Enable2gPreferenceController. This is to align
with TelephonyManager's NETWORK_CLASS_BITMASK_2G.
Bug: b/163168917
Test: m & atest -c Enable2gPreferenceControllerTest
Change-Id: Ia0e099b63a9089be8cd8bfd4211db9eb3c506fc3
Adds (1) Enable2gPreferenceController, the controller for the
"Enable 2G" toggle, and (2) Enable2gPreferenceControllerTest,
the corresponding unit tests.
Test: manul & atest -c Enable2gPreferenceControllerTest
Bug: b/163168917
Change-Id: Ib827cfcfd96fdea77b586c92ae0ec5b2bd5818c3