examples/vhost: fix header copy to discontiguous desc buffer

In the loop to copy virtio-net header to the descriptor buffer,
destination pointer was incremented instead of the source
pointer.

Coverity issue: 277240
Fixes: 82c93a567d ("examples/vhost: move to safe GPA translation API")

Signed-off-by: Maxime Coquelin <maxime.coquelin@redhat.com>

examples/vhost/virtio_net.c

@@ -103,7 +103,7 @@ enqueue_pkt(struct vhost_dev *dev, struct rte_vhost_vring *vr,
 
 			remain -= len;
 			guest_addr += len;
-			dst += len;
+			src += len;
 		}
 
 		desc_chunck_len = desc->len - dev->hdr_len;