Allow vendor_init_readable to persist.sys.usb.usbradio.config

persist.sys.usb.usbradio.config can be read in vendor init scripts.

Bug: 75202311
Bug: 74266614
Test: succeeded building and tested on pixels
Change-Id: Ib07a436dd22b4b445fd114cc1d0df7c3e7a21527
diff --git a/public/property_contexts b/public/property_contexts
index a3702c3..e10a44f 100644
--- a/public/property_contexts
+++ b/public/property_contexts
@@ -115,6 +115,7 @@
 vold.post_fs_data_done u:object_r:exported2_vold_prop:s0 exact int
 
 # vendor-init-readable|vendor-init-actionable
+persist.sys.usb.usbradio.config u:object_r:exported3_system_prop:s0 exact string
 sys.retaildemo.enabled u:object_r:exported3_system_prop:s0 exact int
 
 # vendor-init-settable|vendor-init-actionable