Do endianess conversion on QueueState::used_idx

QueueState::used_idx provides access to a field from the raw
virtqueue, so it needs endianess conversion. Let's add it here.

Signed-off-by: Sergio Lopez <slp@redhat.com>

Author: slp

crates/virtio-queue/src/state.rs

@@ -318,6 +318,7 @@ impl QueueStateT for QueueState {
             .ok_or(Error::AddressOverflow)?;
 
         mem.load(addr, order)
+            .map(u16::from_le)
             .map(Wrapping)
             .map_err(Error::GuestMemory)
     }