virtio-console: Only queue buffers we intend to read

This may help with an outstanding issue where a Bluetooth device became
unstable after a change to crosvm. It's possible that data from the host
was being written into u-boot buffers and then being dropped.

Bug: b/360926085
Test: launch_cvd --resume=false --bootloader=...
Change-Id: I886f2fef150f213b41a7a317d22a89051294c36f
1 file changed