dbus: Fix SignalChange property

SignalChange should be defined as a property of an interface.
Previously, it was incorrectly defined as a property of P2P peers.

Fixes: 7a7ce95746 ("dbus: Emit more information over D-Bus")
Signed-off-by: David Ruth <druth@chromium.org>

doc/dbus.doxygen

@@ -1147,6 +1147,12 @@ fi.w1.wpa_supplicant1.CreateInterface.
       <li>
 	<h3>MACAddress - ay - (read)</h3>
 	<p>MAC address of the interface</p>
+      </li>
+
+      <li>
+	<h3>SignalChange - "a{sv}" - (read)</h3>
+	<p>Signal and quality properties of the interface</p>
+      </li>
     </ul>
 
 \subsection dbus_interface_signals Signals

wpa_supplicant/dbus/dbus_new.c

@@ -4023,6 +4023,11 @@ static const struct wpa_dbus_property_desc wpas_dbus_interface_properties[] = {
 	  NULL,
 	  NULL,
 	},
+	{ "SignalChange", WPAS_DBUS_NEW_IFACE_INTERFACE, "a{sv}",
+	  wpas_dbus_getter_signal_change,
+	  NULL,
+	  NULL
+	},
 	{ NULL, NULL, NULL, NULL, NULL, NULL }
 };
 
@@ -4620,11 +4625,6 @@ static const struct wpa_dbus_property_desc wpas_dbus_p2p_peer_properties[] = {
 	  NULL,
 	  NULL
 	},
-	{ "SignalChange", WPAS_DBUS_NEW_IFACE_INTERFACE, "a{sv}",
-	  wpas_dbus_getter_signal_change,
-	  NULL,
-	  NULL
-	},
 	{ NULL, NULL, NULL, NULL, NULL, NULL }
 };