* grub-core/net/net.c (receive_packets): Decrease the stop to 10
packets but stop only if stop condition is satisfied.
(grub_net_fs_read_real): Call packets_pulled after real read. Use
`stall' instead of `eof' as stop condition.
* grub-core/net/http.c (parse_line): Set `stall' on EOF.
(http_err): Likewise.
* grub-core/net/tftp.c (ack): Replace the first argument with data
instead of socket.
(tftp_receive): Stall if too many packets are in wait queue.
(tftp_packets_pulled): New function.
(grub_tftp_protocol): Set packets_pulled.
* include/grub/net.h (grub_net_packets): New field count.
(grub_net_put_packet): Increment count.
(grub_net_remove_packet): Likewise.
(grub_net_app_protocol): New field `packets_pulled'.
(grub_net): New field `stall'.