wifi: Few minor interface changes

Changes in the CL:
1. Add the buckets scanned bitmask to bgscan.
2. exposed the legacy HAL constants for Bgscan in the HIDL interface.
3. Add a stop method for ring buffer logging.

Bug: 35752950
Bug: 33194311
Test: Compiles
Change-Id: Idb2031c33c5a237d7447410fb733f8e408a17288