net: add qemu_purge_queued_packets()

If net client sends packets asynchronously, it needs to purge its queued
packets in cleanup() so as to prevent sent callbacks being invoked with
a freed client.

Signed-off-by: Mark McLoughlin <markmc@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
diff --git a/net.c b/net.c
index 5b092c7..cea545e 100644
--- a/net.c
+++ b/net.c
@@ -439,6 +439,22 @@
     return ret;
 }
 
+void qemu_purge_queued_packets(VLANClientState *vc)
+{
+    VLANPacket **pp = &vc->vlan->send_queue;
+
+    while (*pp != NULL) {
+        VLANPacket *packet = *pp;
+
+        if (packet->sender == vc) {
+            *pp = packet->next;
+            qemu_free(packet);
+        } else {
+            pp = &packet->next;
+        }
+    }
+}
+
 void qemu_flush_queued_packets(VLANClientState *vc)
 {
     VLANPacket *packet;