Fix response on adapter RequestSession method

Fixes response on adapter RequestSession method to be sent after mode is
changed, if such is necessary. More specifically, change of power off
mode to power on is in question.

Currently response is sent when mode change is confirmed by agent, not
by response from controller. Such may lead to failed CreateDevice method
if it is called quickly enough after RequestSession when controller is
in powered off state.

New session is not created if there is already a session for such D-Bus
message.
diff --git a/src/adapter.c b/src/adapter.c
index 2e11832..b119fd1 100644
--- a/src/adapter.c
+++ b/src/adapter.c
@@ -452,6 +452,20 @@
 	return 0;
 }
 
+static struct session_req *find_session_by_msg(GSList *list, const DBusMessage *msg)
+{
+	GSList *l;
+
+	for (l = list; l; l = l->next) {
+		struct session_req *req = l->data;
+
+		if (req->msg == msg)
+			return req;
+	}
+
+	return NULL;
+}
+
 static int set_mode(struct btd_adapter *adapter, uint8_t new_mode,
 			DBusMessage *msg)
 {
@@ -496,11 +510,18 @@
 
 	DBG("%s", modestr);
 
-	if (msg != NULL)
-		/* Wait for mode change to reply */
-		adapter->pending_mode = create_session(adapter, connection,
-							msg, new_mode, NULL);
-	else
+	if (msg != NULL) {
+		struct session_req *req;
+
+		req = find_session_by_msg(adapter->mode_sessions, msg);
+		if (req) {
+			adapter->pending_mode = req;
+			session_ref(req);
+		} else
+			/* Wait for mode change to reply */
+			adapter->pending_mode = create_session(adapter,
+					connection, msg, new_mode, NULL);
+	} else
 		/* Nothing to reply just write the new mode */
 		adapter->mode = new_mode;
 
@@ -795,16 +816,25 @@
 		return;
 	}
 
-	err = set_mode(req->adapter, req->mode, NULL);
+	err = set_mode(req->adapter, req->mode, req->msg);
 	if (err < 0)
 		reply = btd_error_failed(req->msg, strerror(-err));
-	else
+	else if (!req->adapter->pending_mode)
 		reply = dbus_message_new_method_return(req->msg);
+	else
+		reply = NULL;
 
-	g_dbus_send_message(req->conn, reply);
+	if (reply) {
+		/*
+		 * Send reply immediately only if there was an error changing
+		 * mode, or change is not needed. Otherwise, reply is sent in
+		 * set_mode_complete.
+		 */
+		g_dbus_send_message(req->conn, reply);
 
-	dbus_message_unref(req->msg);
-	req->msg = NULL;
+		dbus_message_unref(req->msg);
+		req->msg = NULL;
+	}
 
 	if (!find_session(req->adapter->mode_sessions, req->owner))
 		session_unref(req);