OvmfPkg/VirtioSerialDxe: respond CONSOLE_PORT with PORT_OPEN

The VirtIO spec states that "Upon receipt of a
VIRTIO_CONSOLE_CONSOLE_PORT message, the driver SHOULD treat the port in
a manner suitable for text console access and MUST respond with a
VIRTIO_CONSOLE_PORT_OPEN message, which MUST have value set to 1". See
https://docs.oasis-open.org/virtio/virtio/v1.3/virtio-v1.3.html#x1-3330002.

The current driver implementation, however, does not comply with that
and only sends PORT_OPEN messages upon receipt of PORT_OPEN messages.
This causes a problem in platforms like Apple's Virtualization
Framework, where PORT_OPEN messages are not sent back to the driver
after CONSOLE_PORT messages are received by the device, a behaviour that
is compliant with the VirtIO specification.

This patch addresses this issue by always responding CONSOLE_PORT
messages with PORT_OPEN messages.

Signed-off-by: Pedro Tôrres <t0rr3sp3dr0@gmail.com>

OvmfPkg/VirtioSerialDxe/VirtioSerial.c

@@ -165,6 +165,7 @@ VirtioSerialRxControl (
         if (Control.Id < MAX_PORTS) {
           VirtioSerialPortSetConsole (Dev, Control.Id);
           Dev->NumConsoles++;
+          VirtioSerialPortSetDeviceOpen (Dev, Control.Id, 1);
         }
 
         break;