allow system server to set log.tag.WifiHAL

On eng and userdebug builds (only), allow system server
to change the value of log.tag.WifiHAL. WifiStateMachine
will set this property to 'D' by default. If/when a user
enables "Developer options -> Enable Wi-Fi Verbose Logging",
WifiStateMachine change log.tag.WifiHAL to 'V'.

BUG=27857554
TEST=manual (see below)

Test detail
1. on user build:
   $ adb shell setprop log.tag.WifiHAL V
   $ adb shell getprop log.tag.WifiHAL
   <blank line>
   $ adb bugreport | grep log.tag.WifiHAL
   <11>[  141.918517] init: avc:  denied  { set } for property=log.tag.WifiHAL pid=4583 uid=2000 gid=2000 scontext=u:r:shell:s0 tcontext=u:object_r:wifi_log_prop:s0 tclass=property_service permissive=0
   <11>[  141.918566] init: sys_prop: permission denied uid:2000  name:log.tag.WifiHAL
2. on userdebug build:
   $ adb shell getprop log.tag.WifiHAL
   $ <blank line>
   $ adb shell setprop log.tag.WifiHAL V
   $ adb shell getprop log.tag.WifiHAL
   V
3. on userdebug build with modified WifiStateMachine:
   $ adb shell getprop log.tag.WifiHAL
   D

Change-Id: I9cdd52a2b47a3dd1065262ea8c329130b7b044db

property.te

@@ -12,6 +12,7 @@ type net_radio_prop, property_type, core_property_type;
 type system_radio_prop, property_type, core_property_type;
 type system_prop, property_type, core_property_type;
 type vold_prop, property_type, core_property_type;
+type wifi_log_prop, property_type, log_property_type;
 type ctl_bootanim_prop, property_type;
 type ctl_default_prop, property_type;
 type ctl_dumpstate_prop, property_type;

property_contexts

@@ -33,6 +33,7 @@ debug.                  u:object_r:debug_prop:s0
 debug.db.               u:object_r:debuggerd_prop:s0
 dumpstate.              u:object_r:dumpstate_prop:s0
 log.                    u:object_r:log_prop:s0
+log.tag.WifiHAL         u:object_r:wifi_log_prop:s0
 service.adb.root        u:object_r:shell_prop:s0
 service.adb.tcp.port    u:object_r:shell_prop:s0
 

shell.te

@@ -64,6 +64,7 @@ set_prop(shell, dumpstate_prop)
 set_prop(shell, debug_prop)
 set_prop(shell, powerctl_prop)
 userdebug_or_eng(`set_prop(shell, log_prop)')
+userdebug_or_eng(`set_prop(shell, wifi_log_prop)')
 
 # systrace support - allow atrace to run
 allow shell debugfs_tracing:dir r_dir_perms;

system_server.te

@@ -319,6 +319,7 @@ set_prop(system_server, debug_prop)
 set_prop(system_server, powerctl_prop)
 set_prop(system_server, fingerprint_prop)
 set_prop(system_server, device_logging_prop)
+userdebug_or_eng(`set_prop(system_server, wifi_log_prop)')
 
 # ctl interface
 set_prop(system_server, ctl_default_prop)