GCS_MAVLINK: added check_payload_size() method

this saves flash by moving common code to cpp

libraries/GCS_MAVLink/GCS.cpp

@@ -356,3 +356,15 @@ void gcs_out_of_space_to_send(mavlink_channel_t chan)
 {
     gcs().chan(chan)->out_of_space_to_send();
 }
+
+/*
+  check there is enough space for a message
+ */
+bool GCS_MAVLINK::check_payload_size(uint16_t max_payload_len)
+{
+    if (txspace() < unsigned(packet_overhead()+max_payload_len)) {
+        gcs_out_of_space_to_send(chan);
+        return false;
+    }
+    return true;
+}

libraries/GCS_MAVLink/GCS.h

@@ -38,6 +38,7 @@
 // macros used to determine if a message will fit in the space available.
 
 void gcs_out_of_space_to_send(mavlink_channel_t chan);
+bool check_payload_size(mavlink_channel_t chan, uint16_t max_payload_len);
 
 // important note: despite the names, these messages do NOT check to
 // see if the payload will fit in the buffer.  They check to see if
@@ -61,7 +62,7 @@ void gcs_out_of_space_to_send(mavlink_channel_t chan);
 // immediately return false from the current function if there is no
 // room to fit the mavlink message with id id on the current object's
 // output
-#define CHECK_PAYLOAD_SIZE(id) if (txspace() < unsigned(packet_overhead()+MAVLINK_MSG_ID_ ## id ## _LEN)) { gcs_out_of_space_to_send(chan); return false; }
+#define CHECK_PAYLOAD_SIZE(id) if (!check_payload_size(MAVLINK_MSG_ID_ ## id ## _LEN)) return false
 
 // CHECK_PAYLOAD_SIZE2 - macro which inserts code which will
 // immediately return false from the current function if there is no
@@ -187,6 +188,8 @@ public:
         return MIN(_port->txspace(), 8192U);
     }
 
+    bool check_payload_size(uint16_t max_payload_len);
+
     // this is called when we discover we'd like to send something but can't:
     void out_of_space_to_send() { out_of_space_to_send_count++; }