sepolicy: Relabel wifi. properties as wifi_prop

 * These properties are used by the wifi hal and it works as expected on
   devices with compatible property. However, on devices without
   compatible property, these prperties are labeled as "default_prop"
   because public/property_contexts is not used. Thus they can't be set
   by the hal.
 * To tackle the problem, label them as "wifi_prop" in
   private/property_contexts which also works on devices without compatible
   property. The label will be overridden later by
   public/property_contexts rules if exist.

Change-Id: If8b8bd5bea64f2ea08864cc62f6dc405cb394e00
diff --git a/private/property_contexts b/private/property_contexts
index b2b6abc..6511668 100644
--- a/private/property_contexts
+++ b/private/property_contexts
@@ -158,6 +158,7 @@
 ro.dalvik.              u:object_r:dalvik_prop:s0
 
 # Shared between system server and wificond
+wifi.                   u:object_r:wifi_prop:s0
 wlan.                   u:object_r:wifi_prop:s0
 
 # Lowpan properties