AP_OADatabase: send_adsb uses vehicle's current altitude

libraries/AC_Avoidance/AP_OADatabase.cpp

@@ -341,6 +341,12 @@ void AP_OADatabase::send_adsb_vehicle(mavlink_channel_t chan, uint16_t interval_
         return;
     }
 
+    // use vehicle's current altitude
+    Location current_loc;
+    if (!AP::ahrs().get_position(current_loc)) {
+        current_loc.alt = 0;
+    }
+
     const uint8_t chan_as_bitmask = 1 << chan;
     const char callsign[9] = "OA_DB";
 
@@ -381,7 +387,7 @@ void AP_OADatabase::send_adsb_vehicle(mavlink_channel_t chan, uint16_t interval_
             item_loc.lat,
             item_loc.lng,
             0,                          // altitude_type
-            0,                          // altitude is always zero
+            current_loc.alt,            // use vehicle's current altitude
             0,                          // heading
             0,                          // hor_velocity
             0,                          // ver_velocity