Found by: Coverity scan.
CID: 96639, 96647

While adding tcp window scaling support I was finding that I'd get some packet
loss or reordering when transferring from large distances and grub would just
timeout.  This is because we weren't ack'ing when we got our OOO packet, so the
sender didn't know it needed to retransmit anything, so eventually it would fill
the window and stop transmitting, and we'd time out.  Fix this by ACK'ing when
we don't find our next sequence numbered packet.  With this fix I no longer time
out.  Thanks,
Signed-off-by: Josef Bacik <jbacik@fb.com>

Using the http module to download config files, produces memory errors,
after the config file is downloaded.

The error was traced to the tcp stack in grub-core/net/tcp.c. The wrong
netbuff pointer was being freed in the clean up loop.

Changing the code to free the correct netbuff pointer removes the runtime
error.

Closes 42765.

	Just "packed" doesn't always pack the way we expect.

	* grub-core/lib/backtrace.c: Likewise.
	* grub-core/net/ip.c: Likewise.
	* grub-core/net/tcp.c: Likewise.
	* grub-core/net/udp.c: Likewise.

	* grub-core/net/http.c (parse_line): Handle response 206.
	(http_receive): Stall if too many packets are in the queue.
	(http_establish): Fix range header.
	(http_seek): Fix double free.
	(http_close): Likewise.
	(http_packets_pulled): New function.
	(grub_http_protocol): Set http_seek
	* grub-core/net/tcp.c (grub_net_tcp_socket): New field `i_stall'.
	(ack_real): Set window depending on i_stall.
	(grub_net_send_tcp_packet): Likewise.
	(grub_net_tcp_stall): New function.
	(grub_net_tcp_unstall): Likewise.
	* include/grub/net/tcp.h (grub_net_tcp_stall): New proto.
	(grub_net_tcp_unstall): Likewise.

	* include/grub/net.h (grub_net_poll_cards): New argument stop_condition.
	All users updated.
	* grub-core/net/arp.c (have_pending): New var.
	(pending_req): Likewise.
	(grub_net_arp_send_request): Fill pending_req and use have_pending as
	stop indicator.
	(grub_net_arp_receive): Set have_pending.
	* grub-core/net/dns.c (recv_data): New field stop.
	(recv_hook): Set stop.
	(grub_net_dns_lookup): Init stop and use as stop condition.
	* grub-core/net/http.c (http_establish): Use headers_recv as stop
	condition.
	* grub-core/net/net.c (grub_net_poll_cards): New argument
	stop_condition. Stop when it goes true.
	* grub-core/net/tcp.c (grub_net_tcp_open): Use `established' as stop
	indicator.
	* grub-core/net/tftp.c (tftp_open): Use `have_oack' as stop indicator.

	on it.

	compact and more efficient code.

	* grub-core/kern/list.c (grub_list_push): Moved from here ...
	* include/grub/list.h (grub_list_push): ... to here. Set prev.
	(grub_list_remove): Moved from here ...
	* include/grub/list.h (grub_list_remove): ... here. Use and set prev.
	(grub_prio_list_insert): Set prev.
	* include/grub/list.h (grub_list): Add prev. All users updated.

    warning.