device_iot_config: Fix hwasan issues in tests

Fixes some uninitialized mock functions and the initial
state of the config and config_timer variables.

Bug: 266269224
Tag: #feature
Test: atest bluetooth_test_gd
BYPASS_LONG_LINES_REASON: Bluetooth likes 120 lines

Change-Id: I8af3b0f05584075d94729f2996e4d41ab746a280