GCS_MAVLink: add route mask for blocking MAVlink forwading

libraries/GCS_MAVLink/GCS.h

@@ -185,7 +185,12 @@ public:
       This is a no-op if no routes to components have been learned
     */
     static void send_to_components(const mavlink_message_t* msg) { routing.send_to_components(msg); }
-
+    
+    /*
+      allow forwarding of packets / heartbeats to be blocked as required by some components to reduce traffic
+    */
+    static void disable_channel_routing(mavlink_channel_t chan) { routing.no_route_mask |= (1U<<(chan-MAVLINK_COMM_0)); }
+    
     /*
       search for a component in the routing table with given mav_type and retrieve it's sysid, compid and channel
       returns if a matching component is found

libraries/GCS_MAVLink/MAVLink_routing.cpp

@@ -254,11 +254,14 @@ void MAVLink_routing::learn_route(mavlink_channel_t in_channel, const mavlink_me
 void MAVLink_routing::handle_heartbeat(mavlink_channel_t in_channel, const mavlink_message_t* msg)
 {
     uint16_t mask = GCS_MAVLINK::active_channel_mask();
-
+    
     // don't send on the incoming channel. This should only matter if
     // the routing table is full
     mask &= ~(1U<<(in_channel-MAVLINK_COMM_0));
-
+    
+    // mask out channels that do not want the heartbeat to be forwarded
+    mask &= ~no_route_mask;
+    
     // mask out channels that are known sources for this sysid/compid
     for (uint8_t i=0; i<num_routes; i++) {
         if (routes[i].sysid == msg->sysid && routes[i].compid == msg->compid) {

libraries/GCS_MAVLink/MAVLink_routing.h

@@ -17,6 +17,8 @@
  */
 class MAVLink_routing
 {
+    friend class GCS_MAVLINK;
+    
 public:
     MAVLink_routing(void);
 
@@ -51,7 +53,10 @@ private:
         mavlink_channel_t channel;
         uint8_t mavtype;
     } routes[MAVLINK_MAX_ROUTES];
-
+    
+    // a channel mask to block routing as required
+    uint8_t no_route_mask;
+    
     // learn new routes
     void learn_route(mavlink_channel_t in_channel, const mavlink_message_t* msg);