vhost-scsi: Include prot_bytes into expected data transfer length

This patch updates vhost_scsi_get_tag() to accept the combined
expected data transfer length + T10 PI bytes as the value passed
into target_submit_cmd().

This is required now that target-core logic in commit 14ef9200
expects to subtract se_cmd->prot_length from se_cmd->data_length.

Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Michael S. Tsirkin <mst@redhat.com>
Cc: Martin K. Petersen <martin.petersen@oracle.com>
Cc: Sagi Grimberg <sagig@mellanox.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>