vm-virtio: Rename epoll_thread to epoll_threads

Now that we unified epoll_thread to potentially be a vector of threads,
it makes sense to make it a plural field.

Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>

vm-virtio/src/vhost_user/blk.rs

@@ -47,7 +47,7 @@ pub struct Blk {
     queue_sizes: Vec<u16>,
     queue_evts: Option<Vec<EventFd>>,
     interrupt_cb: Option<Arc<dyn VirtioInterrupt>>,
-    epoll_thread: Option<Vec<thread::JoinHandle<result::Result<(), DeviceError>>>>,
+    epoll_threads: Option<Vec<thread::JoinHandle<result::Result<(), DeviceError>>>>,
     paused: Arc<AtomicBool>,
 }
 
@@ -130,7 +130,7 @@ impl Blk {
             queue_sizes: vec![vu_cfg.queue_size; vu_cfg.num_queues],
             queue_evts: None,
             interrupt_cb: None,
-            epoll_thread: None,
+            epoll_threads: None,
             paused: Arc::new(AtomicBool::new(false)),
         })
     }
@@ -284,7 +284,7 @@ impl VirtioDevice for Blk {
                 ActivateError::BadActivate
             })?;
 
-        self.epoll_thread = Some(epoll_threads);
+        self.epoll_threads = Some(epoll_threads);
 
         Ok(())
     }