Bluetooth: host: Document privacy-disabled directed advertising reports

Document why a privacy-disabled scanner will not notify about directed
advertising reports. This is the default behaviour of the
privacy-disabled scanner. In order to receive the reports the option
BT_SCAN_WITH_IDENTITY must be enabled.

Signed-off-by: Joakim Andersson <joakim.andersson@nordicsemi.no>

include/bluetooth/bluetooth.h

@@ -509,6 +509,13 @@ struct bt_le_scan_cb {
  *  Start LE scanning with given parameters and provide results through
  *  the specified callback.
  *
+ *  Note: The LE scanner by default does not use the Identity Address of the
+ *        local device when :option:`CONFIG_BT_PRIVACY` is disabled. This is to
+ *        prevent the active scanner from disclosing the identity information
+ *        when requesting additional information from advertisers.
+ *        In order to enable directed advertiser reports then
+ *        :option:`CONFIG_BT_SCAN_WITH_IDENTITY` must be enabled.
+ *
  *  @param param Scan parameters.
  *  @param cb Callback to notify scan results. May be NULL if callback
  *            registration through @ref bt_le_scan_cb_register is preferred.

subsys/bluetooth/host/Kconfig

@@ -484,8 +484,10 @@ config BT_SCAN_WITH_IDENTITY
 	  Enable this if you want to perform active scanning using the local
 	  identity address as the scanner address. By default the stack will
 	  always use a non-resolvable private address (NRPA) in order to avoid
-	  disclosing local identity information. However, if the use case
-	  requires disclosing it then enable this option.
+	  disclosing local identity information. By not scanning with the
+	  identity address the scanner will receive directed advertise reports
+	  for for the local identity. If this use case is required, then enable
+	  this option.
 
 config BT_DEVICE_NAME_DYNAMIC
 	bool "Allow to set Bluetooth device name on runtime"