hostapd(hidl): Add helper functions for writing config file

The HIDL interface for hostapd is a wrapper used to create hostapd conf file.
This file will be then be passed to the hostapd core to avoid
duplication of the conf parsing.

Note: This is a port of the methods in HostapdManager.

Bug: 36646171
Test: Compiles with CONFIG_CTRL_IFACE_HIDL=y in android.config
Change-Id: If11e3f795c05f34442566343ae02bc2a385890a6
diff --git a/hostapd/android.config b/hostapd/android.config
index 3e40aa1..9dfdb28 100644
--- a/hostapd/android.config
+++ b/hostapd/android.config
@@ -213,4 +213,4 @@
 
 # Add support for Hidl control interface
 # Only applicable for Android platforms.
-CONFIG_CTRL_IFACE_HIDL=n
+CONFIG_CTRL_IFACE_HIDL=y