af_iucv: change net_device handling for HS transport

This patch saves the net_device in the iucv_sock structure during
bind in order to fasten skb sending.
In addition some other small improvements are made for HS transport:
   - error checking when sending skbs
   - locking changes in afiucv_hs_callback_txnotify
   - skb freeing in afiucv_hs_callback_txnotify
And finally it contains code cleanup to get rid of iucv_skb_queue_purge.

Signed-off-by: Ursula Braun <ursula.braun@de.ibm.com>
Signed-off-by: Frank Blaschka <frank.blaschka@de.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/net/iucv/af_iucv.h b/include/net/iucv/af_iucv.h
index 0954ec9..a151788 100644
--- a/include/net/iucv/af_iucv.h
+++ b/include/net/iucv/af_iucv.h
@@ -113,6 +113,7 @@
 	spinlock_t		accept_q_lock;
 	struct sock		*parent;
 	struct iucv_path	*path;
+	struct net_device	*hs_dev;
 	struct sk_buff_head	send_skb_q;
 	struct sk_buff_head	backlog_skb_q;
 	struct sock_msg_q	message_q;