virtio-devices: Add helper to VirtioCommon for EventFd duplication

Add a helper to VirtioCommon which returns duplicates of the EventFds
for kill and pause event.

Signed-off-by: Rob Bradford <robert.bradford@intel.com>

virtio-devices/src/vsock/device.rs

@@ -418,26 +418,7 @@ where
         queue_evts: Vec<EventFd>,
     ) -> ActivateResult {
         self.common.activate(&queues, &queue_evts, &interrupt_cb)?;
-        let kill_evt = self
-            .common
-            .kill_evt
-            .as_ref()
-            .unwrap()
-            .try_clone()
-            .map_err(|e| {
-                error!("failed to clone kill_evt eventfd: {}", e);
-                ActivateError::BadActivate
-            })?;
-        let pause_evt = self
-            .common
-            .pause_evt
-            .as_ref()
-            .unwrap()
-            .try_clone()
-            .map_err(|e| {
-                error!("failed to clone pause_evt eventfd: {}", e);
-                ActivateError::BadActivate
-            })?;
+        let (kill_evt, pause_evt) = self.common.dup_eventfds();
 
         let mut handler = VsockEpollHandler {
             mem,