fix(vsock): bring back the debug line in muxer.rs

- the test_cycled_snapshot_restore test checks for its existence in the
  output

Signed-off-by: aerosouund <aerosound161@gmail.com>

Author: aerosouund

src/vmm/src/devices/virtio/vsock/unix/muxer.rs

@@ -197,6 +197,7 @@ impl VsockChannel for VsockMuxer {
                     });
                 }
 
+                debug!("vsock muxer: RX pkt: {:?}", pkt.hdr);
                 match res {
                     Ok(read_res) => {
                         // the read was buffered into an intermediate vector and this