libkrunfw: Add virtio-CAN driver support

Add virtio CAN driver patch v13 from upstream kernel mailing
list to enable vhost-user CAN device support in libkrun.
The driver implements a complete CAN bus interface over
Virtio transport, supporting both CAN Classic and CAN-FD.

Changes:
  - Add patch 0027-can-virtio-Add-virtio-CAN-driver.patch (v13
    from lore.kernel.org/virtualization)
  - Enable CAN kernel configs

Fixes:
  - Kernel 6.12 compatibility fix for can_priv structure access:
    change can.fd.data_bittiming to can.data_bittiming (struct
    layout changed in kernel 6.13+)
  - Fix FORTIFY_SOURCE panic in virtio_can_start_xmit: set
    can_tx_msg->tx_out.length before memcpy() to satisfy
    __counted_by_le() buffer bounds checking.

The driver has been tested with rust-vmm vhost-device-can backend.

Upstream patch authors:
- Matias Ezequiel Vara Larsen <mvaralar@redhat.com>
- Harald Mommer <harald.mommer@oss.qualcomm.com>
- Mikhail Golubev-Ciuchea <mikhail.golubev-ciuchea@oss.qualcomm.com>

Signed-off-by: Dorinda Bassey <dbassey@redhat.com>

Author: Dorinda Bassey

config-libkrunfw_x86_64

@@ -930,7 +930,12 @@ CONFIG_NET_FLOW_LIMIT=y
 # end of Networking options
 
 # CONFIG_HAMRADIO is not set
-# CONFIG_CAN is not set
+CONFIG_CAN=y
+CONFIG_CAN_RAW=y
+CONFIG_CAN_BCM=y
+CONFIG_CAN_GW=y
+CONFIG_CAN_VCAN=y
+CONFIG_CAN_VIRTIO_CAN=y
 # CONFIG_BT is not set
 # CONFIG_AF_RXRPC is not set
 # CONFIG_AF_KCM is not set