[u2f-passthru]: pamu2fcfg command will stuck forever in Guest OS of Qemu
Description of problem:
To use FIDO2 user verification we need to run `pamu2fcfg` command which will stuck forever in Guest OS of Qemu 

Passing `-usb -device u2f-passthru,hidraw=/dev/hidraw2` for U2F-Passthrough
Steps to reproduce:
1. Make you have have plugged Yubikey.
2. In Guest shell install package using following command `sudo apt-get install pamu2fcfg`
3. Run $`pamu2fcfg` command will stuck forever.

**Note:** If I run `pamu2fcfg` in my Ubuntu Host environment it works fine.
Additional information:
**lsusb output:**

**$lusb**

Bus 001 Device 002: ID 46f4:0005 **QEMU U2F USB key**

Bus 001 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub

**Debug Details:**

When pamu2fcfg was launched following will be the call flow.

[u2f_key_recv_from_guest](https://github.com/qemu/qemu/blob/master/hw/usb/u2f.c#L251 "https://github.com/qemu/qemu/blob/master/hw/usb/u2f.c#L251") → [recv_from_guest](https://github.com/qemu/qemu/blob/master/hw/usb/u2f.c#L204 "https://github.com/qemu/qemu/blob/master/hw/usb/u2f.c#L204") → [u2f_passthru_recv_from_guest](https://github.com/qemu/qemu/blob/master/hw/usb/u2f-passthru.c#L332 "https://github.com/qemu/qemu/blob/master/hw/usb/u2f-passthru.c#L332") → [u2f_passthru_read](https://github.com/qemu/qemu/blob/master/hw/usb/u2f-passthru.c#L305 "https://github.com/qemu/qemu/blob/master/hw/usb/u2f-passthru.c#L305") → [u2f_passthru_recv_from_host](https://github.com/qemu/qemu/blob/master/hw/usb/u2f-passthru.c#L329 "https://github.com/qemu/qemu/blob/master/hw/usb/u2f-passthru.c#L329") →[ u2f_transaction_get_from_nonce](https://github.com/qemu/qemu/blob/master/hw/usb/u2f-passthru.c#L272 "https://github.com/qemu/qemu/blob/master/hw/usb/u2f-passthru.c#L272") → [u2f_send_to_guest](https://github.com/qemu/qemu/blob/master/hw/usb/u2f-passthru.c#L302 "https://github.com/qemu/qemu/blob/master/hw/usb/u2f-passthru.c#L302") →[ u2f_pending_in_add](https://github.com/qemu/qemu/blob/master/hw/usb/u2f.c#L207 "https://github.com/qemu/qemu/blob/master/hw/usb/u2f.c#L207") → [main_loop_wait](https://github.com/qemu/qemu/blob/master/system/runstate.c#L783 "https://github.com/qemu/qemu/blob/master/system/runstate.c#L783") (stuck here)

From above call flow looks like guest is waiting for key.

Even I have tried enabling U2F support flag in Qemu while building but that one was not helping either.

**References:**

https://github.com/Yubico/pam-u2f/tree/main

https://www.qemu.org/docs/master/system/devices/usb-u2f.html