SUPL ES Extension - Safer Init and Not After Boot

Safe order of pointer setting and background thread start
Verifying mCallEndElapsedRealtimeMillis is not the initial value

Bug: 112159033
Bug: 115361555
Bug: 125124724
Test: Verified not-after-boot with test code b/115361555#comment14
Test: Reproed NPE with test thread sleep and verify fix
Change-Id: Ic01a5d35d919ccea7934c8384253311261cd0167