qemu: remove overzelaous virtio-net printf

[Marcelo Tosatti <mtosatti@redhat.com>]

When two virtio devices share an interrupt virtio-net floods the console
with "this should not happen" message.

As Anthony points this is not a fatal condition: its possible that the
guest consumed all ring elements between the can_receive check and
actual net_receive call.

Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>

diff --git a/qemu/hw/virtio-net.c b/qemu/hw/virtio-net.c
index a61fdb1..2e57e5a 100644
--- a/qemu/hw/virtio-net.c
+++ b/qemu/hw/virtio-net.c
@@ -119,10 +119,8 @@ static void virtio_net_receive(void *opaque, const uint8_t *buf, int size)
     struct virtio_net_hdr *hdr;
     int offset, i;
 
-    if (virtqueue_pop(n->rx_vq, &elem) == 0) {
-	fprintf(stderr, "virtio_net: this should not happen\n");
+    if (virtqueue_pop(n->rx_vq, &elem) == 0)
 	return;
-    }
 
     if (elem.in_num < 1 || elem.in_sg[0].iov_len != sizeof(*hdr)) {
 	fprintf(stderr, "virtio-net header not in first element\n");