vhost-scsi: support VIRTIO_SCSI_F_HOTPLUG

vhost-scsi: support VIRTIO_SCSI_F_HOTPLUG

So far there isn't way to test host kernel vhost-scsi event queue path,
because VIRTIO_SCSI_F_HOTPLUG isn't supported by QEMU.

virtio-scsi.c and vhost-user-scsi.c already support VIRTIO_SCSI_F_HOTPLUG
as property "hotplug".

Add support to vhost-scsi.c to help evaluate and test event queue.

To test the feature:

1. Create vhost-scsi target with targetcli.

targetcli /backstores/fileio create name=storage file_or_dev=disk01.raw
targetcli /vhost create naa.1123451234512345
targetcli /vhost/naa.1123451234512345/tpg1/luns create /backstores/fileio/storage

2. Create QEMU instance with vhost-scsi.

-device vhost-scsi-pci,wwpn=naa.1123451234512345,hotplug=true

3. Once guest bootup, hotplug a new LUN from host.

targetcli /backstores/fileio create name=storage02 file_or_dev=disk02.raw
targetcli /vhost/naa.1123451234512345/tpg1/luns create /backstores/fileio/storage02

Signed-off-by: Dongli Zhang <dongli.zhang@oracle.com>
Message-Id: <20250203005215.1502-1-dongli.zhang@oracle.com>
Acked-by: Stefano Garzarella <sgarzare@redhat.com>