ivshmem: reset mask on device reset

The interrupt mask is a state value, it should be reset, like the
interrupt status.

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: Claudio Fontana <claudio.fontana@huawei.com>

hw/misc/ivshmem.c

@@ -619,6 +619,7 @@ static void ivshmem_reset(DeviceState *d)
     IVShmemState *s = IVSHMEM(d);
 
     s->intrstatus = 0;
+    s->intrmask = 0;
     ivshmem_use_msix(s);
 }