vsock: Move iter outside of while loop in process_tx_queue.

the iter() function is used for produce a queue iterator to iterate over the descriptors.

But usually, it shouldn't be in the while loop, which might brings more unnecessary overhead.

So move iter outside of the while loop.

Signed-off-by: Li Zebin <cutelizebin@gmail.com>

Author: cutelizebin

crates/vsock/src/vhu_vsock_thread.rs

@@ -607,13 +607,15 @@ impl VhostUserVsockThread {
             None => return Err(Error::NoMemoryConfigured),
         };
 
-        while let Some(mut avail_desc) = vring
-            .get_mut()
-            .get_queue_mut()
+        let mut vring_mut = vring.get_mut();
+
+        let queue = vring_mut.get_queue_mut();
+
+        let mut queue_iter = queue
             .iter(atomic_mem.memory())
-            .map_err(|_| Error::IterateQueue)?
-            .next()
-        {
+            .map_err(|_| Error::IterateQueue)?;
+
+        while let Some(mut avail_desc) = queue_iter.next() {
             used_any = true;
             let mem = atomic_mem.clone().memory();