mavlink_mission: properly initialize padding

This prevents uninitialized padding from being written to dataman.

src/modules/mavlink/mavlink_mission.cpp

@@ -158,7 +158,8 @@ MavlinkMissionManager::load_safepoint_stats()
 int
 MavlinkMissionManager::update_active_mission(dm_item_t dataman_id, uint16_t count, int32_t seq)
 {
-	mission_s mission;
+	// We want to make sure the whole struct is initialized including padding before getting written by dataman.
+	mission_s mission {};
 	mission.timestamp = hrt_absolute_time();
 	mission.dataman_id = dataman_id;
 	mission.count = count;