As in kvm_ioctl and _kvm_ioctl, add
the respective _vm_ioctl for vm_ioctl.

_vm_ioctl invokes an ioctl using the vm fd,
leaving the caller to test the result.
Signed-off-by: NEmanuele Giuseppe Esposito <eesposit@redhat.com>
Message-Id: <20210318151624.490861-1-eesposit@redhat.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>