wifi: Add a new property to indicate active wifi iface

Denial:
libc    : Unable to set property "wifi.active_interface" to "wlan0":
error code: 0x18

Bug: 129506593
Test: Verified that the denial is no longer seen in the logs
Change-Id: Ia345f5df1446e7ba3a44d6e8299bdc1f5f6ad9c8
1 file changed