Allow adbd to set/get persist.adb props, system_server to get.

Bug: b/111434128

Test: getprop persist.adb.wifi.guid
Change-Id: If211c2d00724f62a201dd9c19afc9e894001069f
diff --git a/private/property_contexts b/private/property_contexts
index faa425b..625bf37 100644
--- a/private/property_contexts
+++ b/private/property_contexts
@@ -48,6 +48,7 @@
 security.perf_harden    u:object_r:shell_prop:s0
 service.adb.root        u:object_r:shell_prop:s0
 service.adb.tcp.port    u:object_r:shell_prop:s0
+persist.adb.wifi.       u:object_r:shell_prop:s0
 
 persist.audio.          u:object_r:audio_prop:s0
 persist.bluetooth.      u:object_r:bluetooth_prop:s0