[qemu] 端口重定向

参考：

hostfwd=[tcp|udp]:[hostaddr]:hostport-[guestaddr]:guestport
        Redirect incoming TCP or UDP connections to the host port hostport to the guest IP address guestaddr on
        guest port guestport. If guestaddr is not specified, its value is x.x.x.15 (default first address given by
        the built-in DHCP server). By specifying hostaddr, the rule can be bound to a specific host interface. If no
        connection type is set, TCP is used. This option can be given multiple times.

        For example, to redirect host X11 connection from screen 1 to guest screen 0, use the following:

                  # on the host
                  qemu -net user,hostfwd=tcp:127.0.0.1:6001-:6000 [...]
                  # this host xterm should open in the guest X11 server
                  xterm -display :1

        To redirect telnet connections from host port 5555 to telnet port on the guest, use the following:

                  # on the host
                  qemu -net user,hostfwd=tcp::5555-:23 [...]
                  telnet localhost 5555

        Then when you use on the host telnet localhost 5555, you connect to the guest telnet server.

用于将主机端的端口重定向到客户端的端口上。