floss: Scanner: Rename is_active to is_enabled

Rename it so it won't be confusing along with the scan type (Active scan
and Passive scan).

Bug: 323979740
Tag: #floss
Test: mmm packages/modules/Bluetooth
Test: emerge
Test: build-in-container.py
Flag: EXEMPT, Floss-only changes
Change-Id: I21677c72d6a3f46a3858c09b09734feeab67b1f7