vhost-scsi: Fix max number of virtqueues

vhost-scsi: Fix max number of virtqueues

Qemu takes it's num_queues limit then adds the fixed queues (control and
event) to the total it will request from the kernel. So when a user
requests 128 (or qemu does it's num_queues calculation based on vCPUS
and other system limits), we hit errors due to userspace trying to setup
130 queues when vhost-scsi has a hard coded limit of 128.

This has vhost-scsi adjust it's max so we can do a total of 130 virtqueues
(128 IO and 2 fixed). For the case where the user has 128 vCPUs the guest
OS can then nicely map each IO virtqueue to a vCPU and not have the odd case
where 2 vCPUs share a virtqueue.

Signed-off-by: Mike Christie <michael.christie@oracle.com>
Message-Id: <20220708030525.5065-2-michael.christie@oracle.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Acked-by: Jason Wang <jasowang@redhat.com>