wifi(hal): Use debug property to select one of preset HAL iface combination

This will be useful for testing/debugging STA + STA & AP + AP feature.

Note: I originally planned to read the entire iface combination from the
property (i.e would be much more flexible), but that is way too complex
and error prone. So, instead pre-define some combinations that we would
want to switch between and use the property as an index.

Bug: 173044646
Test: Manual:
i) adb shell "/vendor/bin/sh -c '/vendor/bin/setprop
persist.vendor.debug.wifi.hal.preset_interface_combination_idx 0'"
ii) adb reboot
iii) Ensure that AP + AP was enabled.

Change-Id: Iea63835c39fce78307a056a5ed94efcbd35cdfb6