macvtap: Don't leak unreceived packets when we delete a macvtap device.

To avoid leaking packets in the receive queue.  Add a socket destructor
that will run whenever destroy a macvtap socket.
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/macvtap.c

@@ -339,6 +339,11 @@ static void macvtap_sock_write_space(struct sock *sk)
 		wake_up_interruptible_poll(wqueue, POLLOUT | POLLWRNORM | POLLWRBAND);
 }
 
+static void macvtap_sock_destruct(struct sock *sk)
+{
+	skb_queue_purge(&sk->sk_receive_queue);
+}
+
 static int macvtap_open(struct inode *inode, struct file *file)
 {
 	struct net *net = current->nsproxy->net_ns;
@@ -369,6 +374,7 @@ static int macvtap_open(struct inode *inode, struct file *file)
 	q->sock.ops = &macvtap_socket_ops;
 	sock_init_data(&q->sock, &q->sk);
 	q->sk.sk_write_space = macvtap_sock_write_space;
+	q->sk.sk_destruct = macvtap_sock_destruct;
 	q->flags = IFF_VNET_HDR | IFF_NO_PI | IFF_TAP;
 	q->vnet_hdr_sz = sizeof(struct virtio_net_hdr);