wifi: Fixes in WifiLegacyHal

Changes:
1. Add |is_started_| flag in WifiLegacyHal to ignore stop/start
requests when they're already in the same state.
2. Detach the event loop thread and remove the class member storing
the thread handle.

While there,
1. Cleanup some logs to better help debug issues.
2. Also fixed the wrong method name used in WifiModeController.

Bug: 33480898
Test: Gtests run successfully.
Change-Id: I913f656206a2ca7a79fb316501c256fcdc32aed9