Update doc of proxyAppPackageName

Fixes: 151088537

Test: doc only and builds
Change-Id: If0c4c6d879a1a35293739838702a33ec770b0ed3
diff --git a/gnss/visibility_control/1.0/IGnssVisibilityControlCallback.hal b/gnss/visibility_control/1.0/IGnssVisibilityControlCallback.hal
index 5a582c2..5ee2923 100644
--- a/gnss/visibility_control/1.0/IGnssVisibilityControlCallback.hal
+++ b/gnss/visibility_control/1.0/IGnssVisibilityControlCallback.hal
@@ -82,6 +82,9 @@
         /**
          * Package name of the Android proxy application representing the non-framework
          * entity that requested location. Set to empty string if unknown.
+         *
+         * For user-initiated emergency use cases, this field must be set to empty string
+         * and the inEmergencyMode field must be set to true.
          */
         string proxyAppPackageName;
 
@@ -157,4 +160,4 @@
      * @return success True if the framework determines that the device is in emergency session.
      */
     isInEmergencySession() generates (bool success);
-};
\ No newline at end of file
+};