hostapd(hidl): Add HIDL interface skeletal code

Adding support for HIDL IPC in hostapd. This CL only adds the skeletal
framework for supporting HIDL interface implementation.

There is also a change in the hostapd.h to fix a C++ compilation error.

Bug: 36646171
Test: Compiles with CONFIG_CTRL_IFACE_HIDL=y in android.config
Change-Id: I4a7047a56f8e9be1ed51f2315df707ef5daddc11
diff --git a/hostapd/CleanSpec.mk b/hostapd/CleanSpec.mk
index 653aebb..5d50cd4 100644
--- a/hostapd/CleanSpec.mk
+++ b/hostapd/CleanSpec.mk
@@ -49,4 +49,5 @@
 # NEWER CLEAN STEPS MUST BE AT THE END OF THE LIST
 # ************************************************
 $(call add-clean-step, rm -rf $(PRODUCT_OUT)/system/bin/hostapd)
+$(call add-clean-step, rm -rf $(PRODUCT_OUT)/vendor/bin/hostapd)
 $(call add-clean-step, rm -rf $(PRODUCT_OUT)/system/bin/hostapd_cli)