mcf_fec: Drop mcf_fec_can_receive

The semantics of .can_receive requires us to flush the queue explicitly
when s->rx_enabled becomes true after it returns 0, but the packet being
queued is not meaningful since the guest hasn't activated the card.
Let's just drop the packet in this case.
Signed-off-by: NFam Zheng <famz@redhat.com>
Reviewed-by: NStefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: NJason Wang <jasowang@redhat.com>
Message-id: 1436955553-22791-8-git-send-email-famz@redhat.com
Signed-off-by: NStefan Hajnoczi <stefanha@redhat.com>

hw/net/mcf_fec.c

@@ -397,12 +397,6 @@ static void mcf_fec_write(void *opaque, hwaddr addr,
     mcf_fec_update(s);
 }
 
-static int mcf_fec_can_receive(NetClientState *nc)
-{
-    mcf_fec_state *s = qemu_get_nic_opaque(nc);
-    return s->rx_enabled;
-}
-
 static ssize_t mcf_fec_receive(NetClientState *nc, const uint8_t *buf, size_t size)
 {
     mcf_fec_state *s = qemu_get_nic_opaque(nc);
@@ -417,7 +411,7 @@ static ssize_t mcf_fec_receive(NetClientState *nc, const uint8_t *buf, size_t si
 
     DPRINTF("do_rx len %d\n", size);
     if (!s->rx_enabled) {
-        fprintf(stderr, "mcf_fec_receive: Unexpected packet\n");
+        return -1;
     }
     /* 4 bytes for the CRC.  */
     size += 4;
@@ -490,7 +484,6 @@ static const MemoryRegionOps mcf_fec_ops = {
 static NetClientInfo net_mcf_fec_info = {
     .type = NET_CLIENT_OPTIONS_KIND_NIC,
     .size = sizeof(NICState),
-    .can_receive = mcf_fec_can_receive,
     .receive = mcf_fec_receive,
 };