WifiStatsUsabilityStats: Expose new duty cycle field

Exposing the HAL API added for STA + STA feature. If a connection is
time slicing due to concurrency, a value < 100% will be populated, else
it will always be 100%.

Updated-PDD: TRUE

Bug: 170305665
Test: atest android.net.wifi.cts
Test: atest android.net.wifi
Test: atest com.android.server.wifi
Change-Id: I7b53598a6bc1b94b9b618f358a0935012fe6979c
7 files changed