att_dispatch: fix bug in round robin between

Author: mringwal

src/ble/att_dispatch.c

@@ -81,16 +81,16 @@ static void att_packet_handler(uint8_t packet_type, uint16_t handle, uint8_t *pa
                 if (subscriptions[index].packet_handler && subscriptions[index].waiting_for_can_send){
                     subscriptions[index].waiting_for_can_send = 0;
                     subscriptions[index].packet_handler(packet_type, handle, packet, size);
-                    // fairness
-                    att_round_robin = 1 - index;
+                    // fairness: prioritize next service
+                    att_round_robin = (index + 1) % ATT_MAX;
                     // stop if client cannot send anymore
                     if (!hci_can_send_acl_le_packet_now()) break;
                 }
             }
             // check if more can send now events are needed
             if (!can_send_now_pending){
                 for (i = 0; i < ATT_MAX; i++){
-                    if (subscriptions[index].waiting_for_can_send){
+                    if (subscriptions[i].waiting_for_can_send){
                         can_send_now_pending = 1;        
                         // note: con_handle is not used, so we can pass in anything
                         l2cap_request_can_send_fix_channel_now_event(0, L2CAP_CID_ATTRIBUTE_PROTOCOL);