message: send_message should send the message even if target_system_id is not 0
diff: @@ -134,14 +134,6 @@ bool UdpConnection::send_message(const mavlink_message_t& message)
  return false;
  }
  - // Some messages have a target system set which allows to send it only
  - // on the matching link.
  - const mavlink_msg_entry_t* entry = mavlink_get_msg_entry(message.msgid);
  - const uint8_t target_system_id =
  - (entry && (entry->flags & MAV_MSG_ENTRY_FLAG_HAVE_TARGET_SYSTEM) ?
  - reinterpret_cast<const uint8_t*>(message.payload64)[entry->target_system_ofs] :
  - 0);
  -
  // Send the message to all the remotes. A remote is a UDP endpoint
  // identified by its <ip, port>. This means that if we have two
  // systems on two different endpoints, then messages directed towards
  @@ -149,10 +141,6 @@ bool UdpConnection::send_message(const mavlink_message_t& message)
  // then expected to ignore messages that are not directed to them.
  bool send_successful = true;
  for (auto& remote : _remotes) {
  - if (target_system_id != 0) {
  - continue;
  - }
  -
  struct sockaddr_in dest_addr {};
  dest_addr.sin_family = AF_INET;
  