Prevent unnecessary waiting APN index reset

The RAT changed event causes waiting APNs set, which triggers
the unnecessary index reset (i.e. always start from the first
non-connectable APN).

Fix: 184315538
Test: Manual
Merged-In: Ia7e2c474c7ad13c016443390fa3db288342ff3dc
Change-Id: Ia7e2c474c7ad13c016443390fa3db288342ff3dc
(cherry picked from commit 7e802d08)