floss: Disable scanning interface when adapter is off

BluetoothGatt scan interface interacts with BTIF asynchronously,
creating a possibility use-after-free when adapter is disabled.
This patch address this issue by gating in BluetoothGatt scanning
related public interface based on adapter state.

Bug: 293615016
Tag: #floss
Test: mmm packages/modules/Bluetooth
Test: disable and enable adapter
Flag: EXEMPT, floss change for ChromeOS only.

Change-Id: Ie9de0edb702c455d115e0f22e68badcc72691e78