Update documentation for currentPhysicalChannelConfigs()

Bug: 73739331
Test: n/a, documentation-only change
Change-Id: Ib35af6bc54ee22aaab2f043f7524548f65af1b82
diff --git a/radio/1.2/IRadioIndication.hal b/radio/1.2/IRadioIndication.hal
index 3d93b98..4caddd9 100644
--- a/radio/1.2/IRadioIndication.hal
+++ b/radio/1.2/IRadioIndication.hal
@@ -57,6 +57,8 @@
     /**
      * Indicates physical channel configurations.
      *
+     * An empty configs list indicates that the radio is in idle mode.
+     *
      * @param type Type of radio indication
      * @param configs Vector of PhysicalChannelConfigs
      */