wifi(implementation): Set prop with the first active iface

This is updated whenever a new STA or AP iface is created & removed.
Also, when the chip is configured.

This property can be read by the rest of the system (including vendor
specific HAL instances) to retrieve the active iface name.

Bug: 129506593
Test: ./data/android.hardware.wifi@1.0-service-tests
Test: Manually verified the property name after wifi on/off & softap
on/off.

Change-Id: Ic1c21fd3a1c6894c797070bf889f705e4cba6dd1