floss: Add floss-only properties for LE scan params during AdvMon

BlueZ has separate LE scan parameters for interval and window
that are used for passive scanning supporting the advertisement
monitor APIs. Add a similar property on Floss to control those
parameters and set the default value to match BlueZ.

Bug: 328278477
Tag: #floss
Test: mmm packages/modules/Bluetooth
Test: Manually inspect snoop logs for LE scan window/interval
Test: Manually check phone hub latency with new parameters
Flag: EXEMPT, floss change for ChromeOS only
Change-Id: I864610fe053fc6af159dfcc0976e175352e3906e