wifi(implementation): Use the active iface for chip operation

For the chip level operations, the actual interface itself does not
matter. So, instead of hard-coding these operations to wlan0 interface,
find the first active interface to use. This will still return wlan0 if
it's active, but if only AP is up (& pinned to wlan1), then it will use
wlan1 instead.

Bug: 129358937
Test: ./data/android.hardware.wifi@1.0-service-tests
Test: Verified manually that SAR commands are now correctly sent down.
Change-Id: I5a6175579027cbb45c09d32633ed81b9f72224dd