Return UNKNOWN code when CHRE is not ready

Test: Unit test
Ignore-AOSP-First: nearby_not_in_aosp_yet
Fix: 263890209
Change-Id: I45b3eec6c83848e129704ed9ec5f2c4a49f982fb
(cherry picked from commit 89346d479390e7bf68f77e0be122da2eaec637be)
6 files changed