virtio-devices, vmm: Always restore virtio devices in paused state

Following the new restore design, it is not appropriate to set every
virtio device threads into a paused state after they've been started.

This is why we remove the line of code pausing the devices only after
they've been restored, and replace it with a small patch in every virtio
device implementation. When a virtio device is created as part of a
restored VM, the associated "paused" boolean is set to true. This
ensures the corresponding thread will be directly parked when being
started, avoiding the thread to be in a different state than the one it
was on the source VM during the snapshot.

Signed-off-by: Sebastien Boeuf <sebastien.boeuf@intel.com>

virtio-devices/src/watchdog.rs

@@ -216,7 +216,7 @@ impl Watchdog {
         state: Option<WatchdogState>,
     ) -> io::Result<Watchdog> {
         let mut last_ping_time = None;
-        let (avail_features, acked_features) = if let Some(state) = state {
+        let (avail_features, acked_features, paused) = if let Some(state) = state {
             info!("Restoring virtio-watchdog {}", id);
 
             // When restoring enable the watchdog if it was previously enabled.
@@ -226,9 +226,9 @@ impl Watchdog {
                 last_ping_time = Some(Instant::now());
             }
 
-            (state.avail_features, state.acked_features)
+            (state.avail_features, state.acked_features, true)
         } else {
-            (1u64 << VIRTIO_F_VERSION_1, 0)
+            (1u64 << VIRTIO_F_VERSION_1, 0, false)
         };
 
         let timer_fd = timerfd_create().map_err(|e| {
@@ -246,6 +246,7 @@ impl Watchdog {
                 avail_features,
                 acked_features,
                 min_queues: 1,
+                paused: Arc::new(AtomicBool::new(paused)),
                 ..Default::default()
             },
             id,